Active Pattern Sets Up Two Chances For Snow Along The East Coast This Week

Hello everyone!

Winter is here and there is plenty of interesting stuff to talk about from a synoptic meteorology perspective. This post will take a more in-depth look at the first of two storms expected to bring at least some snow to parts of the East Coast this week.

via COD NEXLAB

Here’s a glimpse at what I’m seeing on satellite imagery this morning. We have a storm moving through Illinois bringing snow to parts of the Great Lakes and rain to parts of the Northeast. While not directly bringing any wintry weather along the East Coast outside far northern Maine, this system will help set the stage for the next two systems, waiting in the wings over Oregon and Alberta. It will help chip away at the subtropical ridge over the western Atlantic, and it will shove the polar front towards the coast.

This sets up the possibility of cyclogenesis (the formation of a new storm) in the Southeast tomorrow evening as the Oregon disturbance meets up with the lower-level front.

By tomorrow evening, a classic cyclogenesis event will be underway as the upper-level disturbance from Oregon supports the development of a surface wave along the polar front.

via Tomer Burg/PolarWx

North of this surface low, a jet streak (region of extra-fast winds embedded within the larger jet stream) is noted over the Ohio Valley. The jet streak doesn’t move forward as fast as the winds within it, so there are regions near the entrance and exit of the jet where winds aloft are accelerating and decelerating. The acceleration into the jet entrance region, particularly the right entrance region in situations like this, draws near-surface air north and upward into the jet. This circulation will contribute to the northward movement (advection) of moisture from the Gulf of Mexico and the subsequent condensation of much of that moisture into rain/snow north of the low’s track.

The critical question is how this developing storm interacts with the Alberta disturbance as it dives east-southeast towards New England.

via Levi Cowan/TropicalTidbits

Current forecasts show the Oregon disturbance east of the Alberta disturbance on Monday evening as it approaches the East Coast, but not by much. Perhaps more critically, the Alberta disturbance is sliding ESE rather than digging SE. That means that the prevailing flow responsible for steering the Oregon disturbance (and our storm) is more west-southwesterly than southwesterly. The result is a track towards the ENE rather than NE. So this won’t turn into a blockbuster blizzard until it gets up to Newfoundland. That doesn’t mean we don’t still have some unanswered questions about just how far northwest precipitation might be able to reach.

via Levi Cowan/TropicalTidbits

This loop shows the last four forecasts from the NAM model for precipitation and sea level pressure all valid Monday evening. Note that the original forecasts showed low pressure slipping offshore without much if any precipitation over the Northeast. The latest forecast has a solid moderate snow event for much of the coastal Northeast as the low tracks a bit closer to the coast.

A look at upper-level wind forecasts shows a favorable setup for northward moisture advection into the right entrance region of a jet streak that curves right as you move east along its axis (meteorologists call this “anticyclonically curved”).

If only that Alberta disturbance were digging southeast, we could have a nice blizzard on our hands but instead all our relevant features will slide quickly ENE and so too will the precipitation shield. This should produce a solid light-moderate snow event for a swath of Southern New England and adjacent parts of PA/MD.

Here’s a first guess on possible accumulations from this system.

I’m a little more bullish on this system because it’s a setup that often supports a bit of last-minute NW trending (like we saw in the NAM forecast comparison above) thanks to poorly-resolved convective processes off the East Coast. That said, I think I’d probably bet on the lower ends of these ranges at least to start.

The storm quickly departs Tuesday morning leaving very cold air poised to surge into the region.

via Levi Cowan/TropicalTidbits

This is true Arctic air, at least for those of us in Northern New England. This bitter cold airmass will help support heavy snow as our next system approaches on Wednesday.

More on that one later this afternoon.

Jack

Eta Strengthening South Of Cuba, HEaded For Southern Florida

Hello everyone!

After re-emerging into the Caribbean Thursday night and re-organizing into a coherent system yesterday, Eta is now re-strengthening south of Cuba.

via NESIDIS STAR

The storm has assembled some very impressive convection this morning which has pulled the center northeast of forecast expectations. This relocation will have some impacts for the storm’s track but it’s probably more important for Eta’s intensity. By moving the center northeast, the storm has put a bit more distance between itself and an upper-level low over the Gulf of Mexico. That low will be a source of dry air and wind shear in the days to come, both of which are detrimental to a storm’s organization and intensification.

via Tropical Tidbits

Hurricane Hunters have been exploring the storm this morning and found a small region of strong winds right near the storm’s new center NW of Grand Cayman Island. Winds at the surface are estimated to be around 50 mph as I write this at 11:15 AM EST.

What’s next for Eta? I suspect our current period of intensification will continue until the storm makes landfall in Cuba tonight. Could it briefly reach hurricane strength? It’s definitely within the realm of possibility. Interaction with Cuba should weaken the core a bit. Most likely though, it’ll stay a moderate/strong tropical storm.

via PolarWx

By tomorrow morning, the storm will be getting closer to the upper-level low over Florida. This means that shear and dry air will start ramping up a bit. After running over Cuba, Eta’s core will likely be disrupted which will make it easier for the shear to induce further weakening. That said, a strong outflow channel will be located northeast of the storm and waters between FL and Cuba are still quite warm so we’ll probably see the storm remain more or less at the same intensity (60mph TS to 80 mph hurricane) as it pivots north and northwest around the eastern side of the upper-level low/trough.

Because Eta could very well be a hurricane as it moves near or over southern Florida on Monday, hurricane watches are now up for the Keys and parts of the southern peninsula even though the official NHC forecast shows a maximum intensity near 70mph.

Regardless of Eta’s max winds, rain will be the biggest threat to southern Florida.

The storm’s slow forward motion and large pocket of moisture (despite wrapping some dry air in near the core) mean that most of southern Florida will see at least 5″ of rain over the next few days. Some spots near Miami are expected to see over 10″ of rain! Be prepared for freshwater flooding issues starting tonight and continuing through Thursday.

via Tropical Tidbits

Another issue will be storm surge flooding as gusty east winds push waves and water onshore not just in southern Florida but all the way up the coast to South Carolina. Watch for beach erosion and minor/moderate coastal flooding in these areas as well as the threat of rip currents.

What happens after the storm passes south Florida?

via Tropical Tidbits

The upper-level low mentioned above will keep pulling Eta west until it’s in the Gulf of Mexico, at which point it will probably slow down considerably. Just how far into the Gulf it can move is an open question, but the storm is likely to still retain its large impact footprint so rain and breezy conditions will continue in Florida.

Because the upper-level low and the storm will eventually be co-located, Eta will have plenty of dry air to deal with. This probably means the storm will slowly weaken. However, we’ll have to watch for another round of potential intensification if the storm can end up creating a small pocket of moisture-rich air once the shear settles down mid/late week. Either way, Eta will eventually move northeast once another trough enters the central US so folks in central/northern FL are likely to at least see some breezy rain, and potentially some more significant impacts, before we can finally say goodbye to Eta.

-Jack

Zeta Poses a Significant Threat as it Intensifies en Route to Louisiana

Hello everyone!

In yesterday’s update, I outlined how Zeta was expected to modestly strengthen as it moved through the Gulf of Mexico supported by rich moisture and somewhat warm water before getting slowed down by cooler ocean temperatures and increasing shear as it neared landfall. Unfortunately, the storm has organized and intensified significantly overnight and it appears as though any weakening that occurs right before landfall will be minor and inconsequential.

Imagery via NESDIS STAR

Satellite imagery shows a marked increase in convective intensity and organization overnight. What were once scattered storms are now powerful “hot towers” becoming increasingly symmetric around the center. The once-ragged eye is increasingly well-defined as the updrafts surrounding the center are balanced out by strong descent in the center itself. Additionally, we can see expansive outflow aloft unimpeded (so far) by the trough to the west of the storm. All of these signals point towards a healthy and strengthening hurricane.

Imagery via the Naval Research Lab

Peering underneath the upper-level cirrus shield using microwave satellite imagery, we can see Zeta’s well-defined eye and eyewall flanked by a few robust bands. This means that Zeta’s structure is conducive to continued intensification today. It has plenty of room to continue adding convection so long as ocean temperatures permit.

Speaking of ocean temperatures, I have thought for a few days now that 25N is roughly the northern extent of really supportive warm water. The storm is just now crossing that threshold so I’ll be watching to see if convective activity begins to struggle from here on out.

Data via UMiami

However, the water doesn’t get cold (<26C) until the last 50 miles or so before Louisiana. So it’s possible that favorable jet stream dynamics (upper-level divergence) could help Zeta continue strengthening so long as ocean temperatures aren’t unsupportive of convection. This is the scenario consistent with NHC forecasts and its the scenario folks in the path of the storm should be ready for. At this point, with the storm structure appearing as robust as it is and the storm’s forward motion being so fast, I don’t think we’ll be able to sneak much weakening in during the hours just before landfall.

Zeta will move onshore in southeastern Louisiana this evening around 5-6 PM CDT. The storm will then continue quickly inland towards southern MS/western AL.

High resolution forecast model guidance provides a good look at how Zeta’s wind field will look as it moves ashore even though the numbers on this map will be an underestimation of actual winds. Note that the strongest winds will be focused east of the storm center’s track. This means that places along the Mississippi coastline 30-50 miles east of the center will see significantly stronger winds than parts of Louisiana 10-15 miles west of the center.

Another key item to note is the wind direction. Winds will be out of the southeast across the Gulf of Mexico immediately south of Mississippi. This will funnel water inland and produce significant storm surge. The shape and topography of the coastline in this area is favorable for enhancing storm surge and folks along the MS coast should be prepared for water 6-10 feet above normally dry ground.

Because Zeta is moving so fast, its swath of damaging winds will extend farther inland than most hurricanes.

Even as the storm races through central Alabama and begins to lose its tropical characteristics early tomorrow morning, it will still be producing a region of 40-50 mph winds capable of producing damage to trees and power lines. These winds will move into northern Georgia later tomorrow morning. Folks in these areas should be ready for power outages even after Zeta weakens below hurricane strength.

Zeta’s remnants are still expected to bring snow to interior parts of the Northeast on Friday though the trend in recent model guidance is towards a weaker and less-amplified storm bringing lighter snow to a smaller area. Oh well.

-Jack

Zeta Expected to Regain Hurricane Strength Tonight En Route To a Louisiana Landfall Tomorrow

Hello everyone!

Now that we’re facing another tropical threat, it’s time to revisit this blog. Perhaps I should’ve started these updates earlier but I’ve been trying to clear the to-do list so I can focus on Zeta for the next several days but here we are.

Zeta formed this past weekend in the NW Caribbean after a cluster of shower/thunderstorm activity finally coalesced underneath a sprawling area of upper-level high pressure. The storm almost met the criteria for rapid intensification when it became a hurricane yesterday before making landfall in the Yucatan last night.

Imagery via NESDIS STAR

A look at satellite imagery this afternoon shows a very broad system with a dry slot separating the inner core from the primary outer band. This dry slot exists because air originating over southern Mexico and moving over the Yucatan Peninsula can’t pick up much if any moisture as it travels over land rather than water.

As Zeta continues moving northwest away from the Yucatan, air parcels moving into the storm’s southeastern quadrant will originate over the Bay of Campeche rather than southern Mexico. These parcels will be rich in moisture having traveled over warm water for a considerable time. This will help the storm’s convection redevelop tonight/tomorrow.

Imagery via CIRA SLIDER

Speaking of redevelopment, the process is already underway as seen in this loop. Cloud tops have rapidly been cooling as convection redevelops at the edge of the storm’s center. This ring of thunderstorms will eventually become the storm’s eyewall.

With generally favorable conditions and ongoing convective development, expect Zeta to reintensify into a hurricane tonight as it moves NW then begins to turn off to the north. That turn will take place as the storm begins moving between a strong ridge of high pressure over the Atlantic and a strong upper-level low over Texas as seen in the graphic below.

Both these features will be pulling Zeta northeast so the storm will begin to accelerate tomorrow. By the time it makes landfall, Zeta will be racing at around 30 mph. This is great news from the rainfall perspective as we don’t have to worry about a stalling system dropping inches of rain for days. However, it means that the wind threat will increase because the system won’t have as much time to weaken over the cooler waters immediately south of Louisiana. Additionally, dry air likely won’t have enough time to wrap into the storm’s core before it moves onshore. So while the storm will likely not make landfall at peak intensity, it probably won’t lose a lot of steam between tomorrow morning and landfall tomorrow afternoon/evening.

The current NHC forecast, shown above, expects Zeta to make landfall in SE Louisiana as an 80 mph hurricane tomorrow afternoon/evening. The storm’s biggest threats will be high winds that will continue well inland into MS/AL as well as storm surge near the coast. Surge may exceed 5-8 feet in parts of SE Louisiana that are not protected by the levee system as well as parts of southern Mississippi and the southwestern coast of Alabama.

Another threat to keep an eye on is tornadoes along and east of the storm center track tomorrow afternoon/evening. Remember this is a very large storm so rain/wind/tornadoes in the outer bands will impact regions many miles away from where the center actually makes landfall.

After moving onshore, Zeta will zip through the southeastern US bringing gusty winds and heavy rain to a swath extending from near New Orleans to Birmingham Alabama and eventually into the mountains of TN/NC.

During this time, the storm will lose its tropical characteristics as it merges with a non-tropical storm moving northeast from Texas. The non-tropical system that will emerge once these two entities join forces is expected to bring heavy snow to parts of the Northeast on Friday. Though it’s noteworthy to have the remnants of a hurricane bring snow to parts of the northern US, snow at this point in the season isn’t super unusual in New England and interior New York.

I’ll have another update if warranted tomorrow.

-Jack

Hurricane Delta to Bring Major Impacts To Louisiana Tomorrow

Hello everyone,

Hurricane Delta is moving through the Gulf of Mexico this morning and intensifying slowly as it does so.

Satellite imagery via CIRA SLIDER

The storm is still struggling to become a well-organized hurricane this morning. Wind shear is lighter now than it was yesterday, so it’s not immediately clear to me why we haven’t seen convection take off on the storm’s eastern/northeastern side. Perhaps that will change later today. Either way, the big takeaway from current observational data is that Delta’s footprint has expanded significantly over the past couple days. While this makes extremely rapid intensification harder to pull off, it means that a wider swath of the coastline will experience strong winds and storm surge will be considerably larger.

The modest intensification and significant expansion of Delta’s wind field is best visualized with hourly forecast model data. I made this animation yesterday afternoon but the forecast hasn’t changed meaningfully in the intervening hours.

The same thought applies to the animation below which uses data from yesterday’s model guidance but remains relevant because forecasts haven’t changed much in the time since.

Model graphics from Tomer Burg / PolarWx and Levi Cowan / TropicalTidbits

As Delta turns north today, the biggest question will be how quickly it’s moving. Ensemble members are in excellent agreement about the general track of the storm. Landfall will occur somewhere in SW Louisiana (exact town dependent on wobbles etc.) it’s just a matter of figuring out when. The current NHC forecast calls for landfall sometime late tomorrow afternoon. The range of possible outcomes in my mind is somewhere between midday tomorrow and early Saturday morning. Either way, today’s the last full day of relatively quiet weather during which you can safely prepare for the storm.

While I don’t think this matters all that much in the end, a slower Delta might slide a smidge farther west due to the weakening trough over Texas. But this would probably be on the order of 15-25 miles rather than some big lurch into Texas. If you’re in Houston, I think you can rest easy knowing that the worst of Delta is headed well to your east (though minor impacts are possible).

Now let’s take a look at Delta’s forecast from an impacts-based perspective.

This map is an overview of the National Hurricane Center’s forecast for Delta’s track, intensity, and rain/wind/surge impacts. The areas most seriously impacted by the storm will be along the coast between Lake Charles and Lafayette Louisiana, as well as points inland. Unfortunately, many of these areas are still recovering from the devastation of Hurricane Laura just six weeks ago.

As per usual, storm surge is the biggest concern as Delta moves ashore. This map provides a clearer view of the NHC’s inundation forecast which calls for parts of coastal Louisiana southeast of Lafayette to be under 9+ feet of water sometime Friday evening. If you’re in this area, please heed the instructions of local officials and evacuate if you are told to do so. Surge will cause some issues as far west as Beaumont/Port Arthur and as far east as coastal Mississippi.

High winds will also be of concern near where Delta makes landfall. Our current best guess at Delta’s maximum sustained winds during landfall is somewhere around 100-110 mph. Perhaps if the storm can intensify a bit more today, those numbers might be a little higher. But I’m less concerned by the maximum wind number than I am about the size of the wind field and how fast the storm will be moving. The larger wind field means that more people will experience tropical storm-force and hurricane-force winds even if there aren’t any major-hurricane-force winds right near the core. The storm’s fast forward motion means that strong winds will be able to move farther inland than we’d otherwise expect. Even if you’re 100-200 miles north/northeast of the point of landfall, you should be prepared for strong winds and power outages.

Delta’s fast movement isn’t all bad news. Because the storm won’t be lingering in any given location for very long, the rain threat should be manageable. Our best rainfall forecasts currently indicate the potential for 4-8″ of rain along and just west of Delta’s track. That’ll undoubtedly cause flash flooding issues in spots but we shouldn’t see much if any major/widespread flooding like we did with Sally or other slow-moving storms.

Delta will quickly dissipate over the Tennessee Valley this weekend.

-Jack

Hurricane Delta Rapidly Intensifying in the Caribbean

Hello everyone!

Now that we have yet another active tropical cyclone and I’ve cleared the decks with my other projects a bit, it’s time to revisit this blog. I’ll be providing updates on Hurricane Delta here each day until the storm has made landfall along the northern Gulf Coast sometime Friday night or Saturday morning. As a reminder, you can also find my tropical weather discussions on twitter (@JackSillin), on the Hurricane Tracker App, and on Mark Sudduth’s HurricaneTrack Patreon page.

Delta formed in the Caribbean just 24 hours ago and is already a powerful Category Two hurricane with maximum winds of 100 mph. Satellite imagery shows very intense convective activity occurring in the storm’s small core west of Jamaica.

Imagery via CIRA SLIDER

Though the storm’s eye is not yet readily apparent on satellite imagery, I suspect it will be soon. The reason we can’t see the eye on satellite imagery yet is that the thunderstorms in the eyewall are too intense relative to the strength of the circulation. Basically, the thunderstorms are pushing cirrus into the eye faster than the sinking motion in the eye can clear them out. As the circulation ramps up to match pace with the thunderstorms, sinking in the eye will become stronger and we’ll see an eye clear out. So at this point in a storm’s lifecycle, not being able to see the eye on satellite imagery is a sign of strengthening not weakening.

Imagery via Cayman Islands Weather Service and CIRA SLIDER

Taking a quick look at the storm’s inner core as observed by radar imagery from the Cayman Islands as well as GOES-East satellite imagery, we can see that while the storm has a small and circular eye, there’s a bit of a “hole” in the core on the northeastern side. This is likely due to some very subtle northeasterly shear imparted on the storm by the upper-level high off to its north. The convection we’re seeing in Delta’s eyewall is so intense that I don’t think this shear will slow the storm down much, but perhaps this is why we don’t have an even-stronger hurricane yet.

By this afternoon/evening, that shear should weaken and the environment will be picture-perfect for continued rapid intensification.

Plot via TropicalTidbits

Area-averaged soundings from the HWRF show every environmental box for tropical cyclone intensification checked this evening. Winds will be uniformly around 15kts out of the east-southeast so shear will be very low. The spread between the temperature and the dew point is very low throughout the atmospheric column which means that dry air won’t be of any concern. Strong heat and moisture fluxes from the incredibly warm ocean mean that rising air parcels will be considerably warmer than their surroundings and thus will rise rapidly due to buoyancy. Outside of inner-core fluctuations that are hard to anticipate, there’s nothing stopping Delta from continued RI today.

This is most immediately concerning for Cancun and adjacent parts of the northeastern Yucatan Peninsula, where Delta will arrive early tomorrow morning.

Map via TropicalTidbits

Current forecasts from our suite of high-resolution hurricane models indicate that Delta will make landfall near Cancun as a powerful Category Four hurricane. This is what the official NHC forecast is calling for too. Impacts in this area will include destructive winds of 120-140 mph, storm surge of several feet, and torrential rains capable of causing flash flooding and mudslides. Residents in these areas need to be preparing now for life-threatening conditions beginning later tonight.

While some weakening is expected as Delta interacts with land, the storm’s brisk motion means that it won’t spend much time away from water. By tomorrow afternoon, the storm will be back out over the Gulf of Mexico ready for another round of intensification. While waters won’t be quite as hot as in the Caribbean, the environment over the southern Gulf tomorrow night looks pretty darn similar to that which we’re seeing in the Caribbean today.

On Thursday, the storm will begin turning towards the north in response to southwesterly flow developing aloft ahead of an upper-level trough over Texas.

Map via Tomer Burg / PolarWx

While the confidence in some type of northerly->northeasterly curve is quite high, we don’t yet know exactly where that turn will happen. If it occurs sooner and/or is a bit sharper, the storm’s track could shift a little bit east. If the turn occurs a bit later and/or isn’t quite as dramatic, the storm’s track could shift a bit west. That’s one reason why even though Louisiana has the highest chance of seeing a landfall from Delta, folks anywhere from the Upper Texas coastline to the western Florida Panhandle need to have a very close eye on this storm. The other reason of course is that hurricanes are not point features, and dangerous impacts will extend well away from the center.

Delta will approach the Gulf Coast Friday evening before making landfall sometime Friday night or Saturday morning. During the last 6-12 hours before landfall, the storm will face a few hurdles that are likely to knock a bit off its maximum intensity (whatever that ends up being).

Animation via Tomer Burg / PolarWx

The first hurdle will come in the form of some increased wind shear due to that upper-level trough over Texas. While winds turn southwesterly aloft, they will remain southeasterly closer to the ground. That change in wind direction with height is wind shear, and will put some stress on the hurricane’s vortex. If Delta were a small and newly-formed system (like Marco earlier this year), I’d say that the odds of this shear weakening the storm dramatically before landfall were relatively good. However, when the shear kicks in over Delta, it will be a powerful Category Four hurricane that already has a well-established vortex. Persistent shear can weaken strong hurricanes like this, but it takes some time. These storms don’t just go poof like little Marco did. They take a while to “spin down”. Unfortunately, Delta will be moving quickly at this point in its lifecycle. Even 6-12 hours of wind shear won’t be enough to avoid a powerful hurricane landfall with significant impacts.

Map via NOAA AOML

The second speedbump for Delta will be the decrease in ocean heat (hurricane fuel) over the northern Gulf. This is due to the cooling effect of several cold fronts that have swept through the region in the past few weeks. While the storm is currently enjoying off-the-charts heat over the NW Caribbean, cooler water lurks over the Gulf. There’s enough heat in the southern Gulf (south of 25N) to support a major hurricane, but Delta won’t be able to spend much time north of that without running low on gas.

That said, the forward motion caveat applies here too. Much like a car running out of gas going down the highway, hurricanes don’t stop immediately after moving into cooler waters. It takes time for all that momentum to dissipate. Delta will only have 6-12 hours over this cooler water before making landfall. While that is welcome news in a season where several hurricanes have rapidly intensified right up until landfall, it will not be enough of an impediment to prevent major impacts.

Map via Weathernerds.org

The third speedbump will be dry continental air moving into the storm’s southwestern flank. This dry air will attempt to wrap into and weaken Delta’s core, but I’m skeptical it will have enough time to make a substantial difference. That said, given the southwesterly shear, the dry air may have an easier path into Delta than it did into Laura earlier this year in the same part of the Gulf.

So all that to say that Delta will likely be slowly coming off its peak intensity as it moves towards the Louisiana coastline. Its maximum winds at landfall are likely to be somewhat lower than its maximum winds over the Caribbean or southern Gulf of Mexico. But that does not mean this won’t be an extremely dangerous hurricane for parts of the Louisiana coastline (and perhaps parts of far eastern TX and/or MS/AL/W FL). It’s crucial to remember that the process of hurricanes weakening involves all the momentum they’ve built up slowly becoming less concentrated. So while winds near the center might be decreasing, the overall wind field usually expands to satisfy the conservation of angular momentum. This process is helped along by eyewall replacement cycles, of which Delta is likely to complete at least one.

Residents in Louisiana need to have their hurricane plans ready to go for when watches and warnings are issued in the next couple days.

I’ll leave you with a look at the NHC’s official forecast for Delta which neatly summarizes many of the ideas I’ve discussed here. I cannot stress enough how little you should focus on the icon over Louisiana at 2 AM Saturday being an “H” for Hurricane instead of “M” for Major Hurricane. I can assure you that you will not be able to notice the difference between a 110 mph Category Two and a 115 mph Category Three, and this storm will be extremely dangerous regardless of its maximum sustained winds at landfall.

I’ll have more updates throughout the day on twitter (@JackSillin).

-Jack

Major Hurricane Teddy Churns Through the Atlantic, Likely to Bring Direct Impacts to Both Bermuda and Eastern Canada

Hello everyone!

There’s a whole lot of mayhem continuing to plague the Tropical Atlantic and some portions of the land surrounding it this afternoon.

Imagery via CIRA

We’ve had two more storms, Wilfred and Alpha, named this morning which brings us into the Greek Alphabet for the first time since 2005 and the second time since tropical storm naming began back in 1950. Wilfred is located southeast of Teddy and poses no threat to any landmass. Alpha is barely visible on this image near Portugal where heavy rain and strong winds are ongoing. Meanwhile in the Gulf of Mexico, TD 22 is spinning between Texas and the Yucatan Peninsula. TD 22 does pose a serious threat to Texas in the form of heavy rain, but it will not be the subject of this post. Instead, we’ll focus on Teddy here.

Model data via Tropical Tidbits

Teddy is one of those hurricanes you see on the front cover of meteorology textbooks. It has a circular and nearly symmetrical eye, a ring of extremely intense eyewall thunderstorms, and expansive upper-level outflow in all directions away from the center. As of the 11 AM EDT update from the NHC, Teddy had maximum sustained winds of 130 mph making it a Category Four storm.

Microwave imagery from polar-orbiting satellites lets us peer under the upper-level clouds into the storm’s structure.

Microwave imagery via NRL

The storm’s eyewall is clearly visible using this tool as the ring of red/green surrounding the eye which is visible in bright purple. The northeastern eyewall is clearly much more intense than the southwestern eyewall. That’s due to a bit of southwesterly wind shear the storm is dealing with on the southeastern side of a weak upper-level low. Teddy’s outflow is working to blast a hole in that upper-level low so the storm can continue moving northwest with minimal disruption.

Model data via Tropical Tidbits

The only thing slowing Teddy down prior to its arrival in Bermuda will be interaction with a pool of cold water left by Paulette. This should be enough to knock the storm’s maximum winds down a little bit, but all most of that angular momentum will stick around in the form of an expanding wind field and the balance will be transferred to the ocean in the form of massive waves.

Ensemble guidance via weathernerds.org

Thankfully, most model guidance has the storm sliding just east of Bermuda as it makes its closest approach on Sunday night. That will put the island on the “weaker” side of the storm, and perhaps just outside the eye. However, because the storm’s windfield is so massive, strong winds are basically a lock for the island at this point. It’s just a matter of figuring out whether that’s 50 mph, 75 mph, or 100+ mph.

Model data via Tropical Tidbits

After Bermuda, Teddy is still expected to make a turn to the north or north-northwest as an upper-level low cuts off to the west/northwest of the storm. The exact details of this interaction between the hurricane and the trough are still yet to be determined. That said, guidance has shifted east a bit in the last day or so. That means a direct hit for eastern New England now looks unlikely. Nova Scotia is much more likely to get the brunt of Teddy as it moves onshore as a hurricane rapidly undergoing extratropical transition.

Ensemble plot via Tomer Burg

This is the forecast shown by the majority of EPS ensemble members, though it should be noted that outlier solutions exist both to the west (farther into the Gulf of Maine) and to the east (closer to Sable Island).

Model data via Tropical Tidbits

This is one model depiction of what the storm could look like by Tuesday morning. The shading on the map depicts winds at 10m above the ground. If you don’t have your ruler handy, by this point in the cyclone’s evolution, the storm could have hurricane-force winds extending well over 100 miles from the storm center. So even if the hurricane’s maximum winds weaken dramatically before landfall (that’s expected to happen due to the cool waters in this area), strong winds will have no problem making it onshore.

With this in mind, Nova Scotia needs to be ready for serious impacts from Teddy including heavy rain, strong winds, and storm surge.

The large windfield will also produce massive waves.

Significant wave height forecasts for Tuesday morning are approaching 50 feet near Teddy’s center off Nova Scotia while waves over 10 feet roll onto the East Coast from Maine to Florida and the Bahamas. Near-shore breaking waves will vary in height by exact location, but this shows that the threat for huge waves and all the dangers they pose (beach erosion, rip currents, washing people off the rocks, etc.) is quite high.

-Jack

Hurricane Sally Crawling Slowly Towards The Gulf Coast This Morning

Hello everyone!

The big story in the tropics this morning is still Hurricane Sally which is crawling ever so slowly towards the Gulf Coast.

Imagery via CIRA SLIDER

The storm has been struggling to tighten up its inner core in the face of mid-level dry air and some southwesterly wind shear. Note the lack of cloud cover southwest of the storm’s center compared to the wide expanse of clouds to the east of the center. While the shear is good news for folks in the path of Sally’s inner core, it is bad news for the Florida Panhandle which is seeing torrential rains this morning despite being relatively far from Sally’s center.

Here’s a look at early morning (6:15 CDT) radar imagery of Sally showing a ragged eyewall wrapping about three quarters of the way around the center. The eyewall is open to the southwest which is what we’d expect given the southwesterly wind shear and dry air located west of the system.  Heavy rain and strong winds are now moving into southern Alabama and far southeastern Mississippi and the window of time to prepare safely for the storm has closed accordingly.

Farther east, an intense feeder band has set up from Mobile Alabama to Pensacola Florida and southeast into the Gulf of Mexico. This band will likely linger in this area for the rest of the day today into tonight, and will produce extreme rainfall totals of 1-2 feet along with embedded tornadoes.

Imagery via TropicalTidbits

Most model guidance is now in agreement that Sally’s center moves onshore late tonight near Mobile Bay in Alabama as a Category One or Two storm. This would put the system’s strongest winds and highest surge right over the city of Mobile. It’s important to note that the worst of the surge in Mobile Bay will hit after the eye has passed which is when winds shift from cross-shore to onshore.

Model maps via TropicalTidbits

After moving onshore, Sally will continue northeast tomorrow and Thursday, bringing heavy rain along with it. Folks in N GA and parts of NC/SC should be ready for flooding even though Sally will be rapidly moving towards dissipation at that point.

I’ll be covering this storm in much more detail on twitter today.

-Jack

Parade of Atlantic Tropical Mayhem Continues- Six Other Storms to Watch Excluding Sally

Hello everyone!

The main focus of my coverage in recent days has been on Hurricane Sally which poses a serious threat to the Gulf Coast, but there are six other tropical entities in the Atlantic that bear watching today. Thankfully, none of them pose the level of risk to land that Sally does. This post will briefly examine each of those other systems. Another post will focus on taking an updated look at Sally.

Imagery via CIRA SLIDER

Satellite imagery of the Northwestern Hemisphere clearly highlights each of our disturbances to watch today. Our four named storms in various states of organization plus three disturbances that we’ll have to watch for potential development in the next few days.

Off the East Coast, Paulette continues to move northeast away from any and all landmasses.

Imagery via CIRA SLIDER

The storm was expected to intensify during this part of its journey due to lower shear and favorable interaction with a mid-latitude jet streak over far eastern Canada. However, the storm’s inner core structure is a bit sloppy (a la Sally) and it hasn’t really been able to pull itself together. Regardless, the storm remains quite dangerous for mariners in this part of the North Atlantic.

Paulette’s remaining threat to land will come in the form of large swells along the East Coast today.

This buoy about 50 miles southeast of Nantucket shows swell heights around 8-10 feet this morning with a period (not shown) of 14-15 seconds. That means these waves are packing tons of energy and will be quite dangerous for those that get close to them as they break. If you’re an experienced surfer, have fun riding these waves. For the rest of us, keep a safe distance.

Moving farther out into the Atlantic, we’ll find Tropical Storm Teddy  several hundred miles east of Barbados.

Imagery via CIRA SLIDER

Teddy looks really good on satellite imagery at sunrise this morning, it just needs to focus its intense thunderstorm activity near its center. Once that happens, it should have no trouble intensifying into a major hurricane. The storm is currently in a moist, low-shear atmospheric environment above very warm ocean waters. Its intensity ceiling is very high, and we may see it make a run at Category Four status by this weekend.

Teddy is forecast to move basically due northwest for the next five days, during which time it will not impact land. There’s some uncertainty once we get to the day 4-5 timeframe when some guidance suggests a potential shift in the storm’s track off towards the west-northwest. As of right now, I’m not inclined to see Teddy as a major threat to land but it does bear watching. We’ll revisit this steering pattern after we’re done with Sally.

Northeast of Teddy is tropical storm Vicky.

Imagery via CIRA SLIDER

Sunrise over Vicky reveals a cyclone being acutely impacted by strong southwesterly wind shear. Notice how the storm’s low-level swirl is displaced significantly from its deep thunderstorm activity. This shear is being delivered by a strong upper-level low to the northwest of Vicky and will bring about the system’s rapid demise later today.

Rene became a remnant low yesterday, so this concludes our tour of the active tropical cyclones in the Atlantic not named Sally.

Closer to the African coast we’ll find our next tropical wave to watch for development.

Imagery via CIRA SLIDER

This wave is producing relatively deep convection this morning and it’s starting to coalesce around what might be an incipient center of circulation. The environment surrounding the system is fairly supportive of intensification, and I’d expect to see yet another tropical depression or storm develop from this system in the coming days.

Model forecasts via TropicalTidbits

Most model guidance isn’t too bullish on this system’s future intensity, though the GFS parallel model (new version in beta testing) takes it up to hurricane strength briefly while recurving into the open ocean. No impacts are expected from this system. If named, this will be called Wilfred and will use up the last name on the list for the Atlantic this season. Future storms will then be referred to by the various letters of the Greek Alphabet.

One of those future storms may very well be this feature west-northwest of Portugal.

Imagery via CIRA SLIDER

Satellite imagery shows the system’s frontal features becoming detached from its center where convection is beginning to build. If convection persists for long enough, it will release enough latent heat into the storm’s core for it to be considered a tropical or subtropical storm.

Forecast chart via Bob Hart’s phase space page

This graphic shows the cyclone’s expected evolution from “asymmetric warm core” or subtropical (which is where it is right now) towards “symmetric warm core” or tropical by later today/tomorrow. Even if the storm does become tropical, it will weaken substantially before impacting Portugal in four or five days. But perhaps the storm could snatch the name “Wilfred”, leaving the wave in the eastern Atlantic to become “Alpha”.

Way back in the southwestern Gulf of Mexico, we’re still dutifully watching this system which is producing some shower and thunderstorm activity east of northeastern Mexico.

Imagery via weathernerds.org

The system hasn’t yet been able to focus its thunderstorm activity around a single center, but if this current burst is able to hold through the day today, it could. NHC penciled in a recon flight for this afternoon, but unless it looks like a low-level center might be present, they’ll probably cancel it.

Either way, it doesn’t pose much threat to land in the short-term. We’ll revisit its future in more detail after Sally.

Finally, it appears as though the Atlantic Basin’s tropical cyclone activity is mildly contagious.

Model forecasts via TropicalTidbits

The Mediterranean Sea may join in on the action this week as a low near Libya moves northeast towards Greece. The Mediterranean gets systems like this every once in a while, so this development (if it were to occur) would be unusual but not unprecedented.

More coverage of these systems in the coming days, especially after we’re done with Sally.

-Jack

Sally Steadily Organizing Over the Gulf of Mexico This Morning

Hello everyone!

Yesterday, we talked a lot about how Sally’s intensity forecast was quite uncertain but that the storm was likely to intensify into a hurricane if it was able to wrap deep convection around its low-level center. Unfortunately, that has been happening over the past twelve hours or so, though in fits and starts.

Imagery via CIRA SLIDER

Last night’s convective burst waned a little bit as it ran into shear and dry air to the west of the storm’s circulation, but another burst has taken its place this morning and is once again attempting to wrap around the NW side of the storm. Whether or not it will succeed, only time will tell.

In the meantime, there is a bit of a shift in track guidance that’s worth talking about.

Trend graphic via Brian Tang’s TC page

Yesterday, most guidance took Sally into SE LA before moving NW very near New Orleans then into SW MS or NE LA. Newer model runs are now suggesting the system may turn towards the north before reaching SE LA and instead make landfall in S MS. The HWRF does a particularly good job highlighting this trend, though it would work with any model of your choosing.

Why is this happening? Guidance is making some subtle adjustments to the steering pattern and is also expecting Sally to strengthen a bit faster today.

Model graphic via TropicalTidbits

Remember that the stronger the storm gets, the more it will “feel” the southerly winds aloft that want to push the storm north. Because the storm appears to be strengthening this morning, I have confidence that this eastward trend in guidance is more signal than model noise.

What does that mean for impacts?

Here’s a look at the latest overview map from the NHC. Note the eastward shift in the forecast track from near or just west of New Orleans to near Biloxi Mississippi. The good news is for folks in New Orleans who are now very unlikely to see the worst of Sally’s rain, wind, or surge. Gusts to 40-50 mph will still cause power outage issues, and surge off Lake Pontchartrain (4-6+ feet) will still cause flooding. But given the potential Sally had to push hurricane or major hurricane-force winds through downtown NOLA, this shift in track is very welcome news.

When it comes to shifting tracks for landfalling hurricanes, good news for one area is bad news for another. The bad news is for southern MS, southern AL, and far western FL which will now be closer to the core of Sally as it moves onshore. Rainfall totals here will soar past 20″ as the system slowly crawls onshore. Meanwhile, surge will push into the various bays and inlets and could produce inundation of up to six feet as far west as the AL/FL border. Residents in these areas should be prepared to evacuate today if told to do so by local officials. Remember that storm surge risk is highly localized and depends on very small shifts in track/intensity. The values blanket outlined for large portions of the coastline may not be representative of how much water you see in your backyard.

While the water-related threats from Sally are far more serious than the storm’s winds, portions of the SE LA and S MS coastlines will see hurricane-force winds as the core moves onshore tomorrow. Tropical storm-force winds currently extend up to 125 miles from the storm’s center and will be capable of causing power outages even in areas that do not experience the storm’s core.

Here are a few more maps that show just the surge/rain/wind forecasts individually and are thus a bit easier to read.

Note that the highest surge, heaviest rain, and strongest winds are all focused near and just east of the center’s expected track. If the storm continues to strengthen today and ends up tracking a bit farther east, the worst of the storm would slide from near Biloxi MS closer to Mobile AL. Folks in this area should be preparing as though this were expected to happen. It’s also important to note that even on the storm’s current heading, one to two FEET of rain is expected for much of the MS/AL/W FL panhandles. Even if you don’t get Sally’s worst surge or winds, the rain is going to cause some serious flooding issues.

As the storm moves north on Wednesday, it will rapidly weaken though heavy rains will continue to push inland over MS/AL. The storm should dissipate by Thursday as it moves closer to Georgia.

I’ll have many more updates on Sally on twitter throughout the day. I also plan to do another post later this morning exploring some of the other tropical systems in the Atlantic basin.

-Jack

Jack Sillin's analysis of the latest atmospheric happenings