All posts by Jack Sillin

I’m Jack Sillin, freshman at NYA, snow-lover, enjoyer of the outdoors, and of course, weather geek. My passion for weather began several years ago when I was about six years old on a series of long plane trips while watching countless hours of The Weather Channel. My skills have evolved rapidly in the past few years from excitedly refreshing the radar on the local TV weather page (I’m still guilty of that from time to time…) to waking early to analyze complex charts and graphs every day to produce a forecast. I’m hoping to pursue a career in the NWS someday. Aside from the weather, I’m a big skier and lover of all things cold and snow. I also like to do many other outdoor activities such as hiking and fishing when the snow is no longer around. I can be reached through twitter @JackSillin and via email at

Sally Expected to Impact the New Orleans Area as a Hurricane Tomorrow and Tuesday

Hello everyone!

While there are plenty (seven!) of systems to watch across the tropical Atlantic this morning, our focus remains on Tropical Storm Sally which is expected to intensify into a hurricane before impacting the New Orleans area and adjacent parts of the northern Gulf Coast beginning tomorrow and continuing through Wednesday.

In recent days, I’ve spent considerable time on the blog explaining the meteorological processes working both for and against intensification, as well as pushing the storm in different directions. If you want to dig into the nerdy details of this system’s forecast, feel free to read over last night’s post if you haven’t already. Pretty much all the info there is still current even if the satellite loops are a little stale. This update will focus much more on the system’s expected impacts as it moves onshore somewhere in southeastern Louisiana and/or southern Mississippi.

As a quick reminder, you can sign up via the box on the left sidebar to receive my updates via email the moment they are posted if that’s something you’re interested in.


Our primary guide for this morning’s updates will be the info NHC sent out in their 5 AM EDT advisory on the storm.

This map shows the storm’s expected track, intensity, and rain/wind/surge impacts as well as the watches and warnings in effect as of 5 AM EDT. Click the map for a larger version that’s a bit easier to read. The key idea to take away from this graphic is that serious impacts, especially heavy rain, will extend relatively far from the center of Sally, especially to the east. So folks in the Florida Panhandle and southern Alabama shouldn’t let their guard down despite not being near the center of the cone (or in the case of most of FL, outside the cone entirely).


This map is zoomed in near where Sally is expected to make landfall in southeastern Louisiana and shows the storm’s forecast track, intensity, and storm surge. Note that areas outside the New Orleans levee system could see over nine feet of storm surge inundation as Sally’s circulation pushes water from the Gulf of Mexico west and northwest towards Lake Pontchartrain. As someone unfamiliar with the New Orleans levee system, I do not know which levees might or might not be in danger of failure from a surge of this magnitude. Local officials in this area do have that information, and if they tell you to leave, please make every effort to do so. If you don’t have the resources to evacuate, please get in contact with your local officials who will likely be able to assist you with transportation, accommodations, etc.

Surge will also be an issue well east (and somewhat west) of where Sally moves onshore. Southern Mississippi and parts of southern Alabama could see over six feet of surge if Sally ends up making landfall in SE Louisiana as a hurricane (which is the current NHC forecast). Areas as far east as the Big Bend region of Florida will see surge from Sally in the range of 1-3 feet. This will cause problems in the usual low-lying spots prone to flooding from even “minor” events.


Heavy rainfall will pose an extremely serious threat to parts of SE LA, southern MS, southern AL, and western FL. Light westerly wind shear has pushed most of Sally’s thunderstorm activity to the east of the center which means that heavy rain will extend well east of wherever the center makes landfall. As the map above highlights, 9-12″ of rain is likely as far east as Panama City Florida. This amount of rain, with locally higher amounts (to 20″ or more) will cause serious and widespread flooding. If your area is vulnerable to flooding from heavy rain, consult with information from your local officials and be prepared to evacuate if told to do so.

Heavy rain will also be an issue near the center landfall location in SE Louisiana, but totals will drop off fairly quickly as you head west.


I’ve discussed wind last here because even for those areas expecting hurricane-force winds, what’s happening with the air will be the least of your worries. What’s happening with the water (both rain and surge) is a much bigger threat to your life. That said, strong winds will cause problems along and especially east of Sally’s center track. As of 5 AM EDT, NHC forecasts call for landfall as a 100 mph category two storm. That means that most places near the center of the storm will see sustained winds of 75-85 mph. Remember that the “maximum sustained wind” forecast number really only applies to areas over open water and perhaps some immediately adjacent beachfront locations. It’s also important to keep in mind that you don’t need 100 mph winds to cause serious issues. Even winds of “only” 50 mph will knock down trees and power lines. Winds of 50-75 mph will cause increasingly widespread tree/power line issues and may start to cause some minor structural damage. Winds above 75 mph begin to pose a more serious threat to siding/roofs.


All the above information is based on the best available forecast info we have this morning. But that’s not to say we’re 100% confident about how strong Sally will be at landfall or where exactly it will move onshore.

Recall from yesterday’s post that the environment Sally will occupy starting tonight is extremely favorable for rapid intensification if the storm can wrap convection around its inner core.

Model image via TropicalTidbits

With that in mind, there remains the potential for Sally to strengthen more than currently forecast. I’ve advised my friends in the New Orleans area to prepare as if Sally were making landfall as a Major Hurricane (Category Three) because that outcome is well within the range of reasonable possibilities given the environment. If the northwesterly shear is just light enough to keep the low- and mid-level circulations displaced, and Sally ends up coming onshore as a “weaker” (but still quite dangerous!) hurricane, we can all be thankful it wasn’t worse. Prepare for the reasonable worst-case outcome (Category Three landfall) and hope for the reasonable best-case outcome (low-end Category One or high-end Tropical Storm landfall).

It’s also worth noting again that the category system only takes into account a storm’s maximum sustained wind speed which, as mentioned above, is not representative of the winds most folks (even near the center) will experience, nor does it convey any information about the significantly more dangerous rain/surge threats.

Looks Will Be Deceiving

Even in the scenario where Sally moves onshore as a Category Three hurricane (depicted by the 00z HWRF model as an example), it is not likely to achieve its final form until it’s right at the coastline.

Model image via TropicalTidbits

This image is from that HWRF model run that represents the “reasonable worst-case outcome” for Sally. The forecast map is valid tonight at 8 PM EDT. Note that the system is still a mid-grade tropical storm with the low-level center significantly displaced from the strongest convection. Even if we were to see little organization of the system today, it still has the potential to rapidly intensify tomorrow. You should not wait for the storm to take on the appearance of a “classic” hurricane with a well-defined eye before you take it seriously. By then, it will be too late to do anything but hunker down and hope for the best.

Model animation via TropicalTidbits

This animation shows the HWRF’s prediction of what satellite imagery might look like between now and the storm’s landfall. Note that even in this bullish model depiction of Sally’s intensity, the eye only shows up clearly once the system is directly over New Orleans!

After making landfall, Sally will move slowly north until it dissipates over Mississippi. The slow movement is welcome news from a wind perspective (widespread wind damage will not continue well inland like it did with Laura) but is very bad news from a surge/rainfall perspective. Heavy rain and strong onshore winds will linger into Wednesday even as the storm weakens just inland.

I’ll have updates throughout the day on twitter and will most likely be back here on the blog this evening with an updated look at expected impacts.


TD19 Becomes TS Sally, Expected To Make Landfall As A Hurricane In SE Louisiana Tuesday

Hello everyone!

It’s a very busy evening in the tropics as we watch four active tropical cyclones and two disturbances that might develop in the next five days.

Imagery via NESDIS STAR

Each of our systems is visible on this loop of the tropical Atlantic. From west to east, we have a disturbance in the Gulf (30% chance of development), Sally (near S FL), Paulette (SE of Bermuda), Rene (SE of Paulette), TD 20 (embedded within the Inter-tropical Convergence Zone about half way between Barbados and Africa), and Invest 97L (southwest of the Cabo Verde Islands). If you look at the far eastern edge of the loop, you’ll see the first hints of our next wave set to emerge off Africa in a couple days. Unfortunately, we’ll have to keep an eye on that one too.

This update will focus mostly on Sally because it poses the most serious threat to US interests. If you’re in Bermuda and curious about my analysis of Paulette with a focus on Bermuda impacts, please check out my update on Mark Sudduth’s page earlier this afternoon.

Imagery via NESDIS STAR

Sally has changed little in organization today as it meandered near southern Florida. The system’s low-level center is located a bit west of Naples Florida. Note that this is a bit northwest of the storm’s deep convective activity which is located near the Florida Keys. This indicates that the system’s low- and mid-level centers are still misaligned with the former being northwest of the latter.

For most of last night, that was due to northwesterly shear imparted on the system by an upper-level low to its northwest. This evening, that low is weakening and moving away from the system so I don’t anticipate we’ll see shear continue to be an issue for Sally as we move into tonight.

Image via TropicalTidbits

That said, area-averaged soundings suggest that low-level southeasterly flow will be a bit stronger near the surface than farther aloft. This actually is a bit of a northwesterly shear signal even though there aren’t really any northwesterly winds (excluding the 5kts at 150 mb) in the atmosphere. So while the low-level center will continue to “run ahead” of most of the convection, without a strong force pushing storms to the east of the center, I’d expect to see thunderstorm activity develop and persist near the center starting later tonight or tomorrow morning.

Why wait that long? The primary factor holding back convection on the north/northwest side of Sally isn’t any upper-level wind issue or mid-level moisture issue, it’s actually a low-level problem.

I made this graphic earlier today so the radar data isn’t “fresh” but it highlights the process well. Low-level air parcels (think right near the surface) flowing into the northwestern side of Sally have spent considerable time over the Florida Peninsula instead of over the warm waters of the Gulf of Mexico. As a result, they’re a bit drier than they need to be to support convection. Parcels flowing into the southern side of the system have spent considerable time over the Gulf of Mexico picking up moisture and heat from the warm water beneath them. As a result, these parcels are jam packed with energy to support convection in a way that those parcels originating over Florida are not.

As Sally continues moving west-northwest into the Gulf of Mexico, I suspect we’ll see convection start to develop a bit more on the northern side especially once the system passes Tampa Bay’s latitude. At that point. there will be much more open water to the storm’s northeast for parcels flowing into the northern side of the system to pass over and acquire heat+moisture.

Imagery via TropicalTidbits

The HWRF model, which is a high-resolution model specifically designed to predict hurricanes, shows this idea well. It depicts Sally struggling to organize until it passes north of 28N which is about where Tampa is. After that, it has a bit more “room to breathe” on the northern side and as a result is able to strengthen quite a bit more.

Image via TropicalTidbits

A look at the upper-level environment shows a setup extremely conducive for intensification come tomorrow evening. The storm will be located under an upper-level anticyclone well-positioned to vent the system in the upper levels of the atmosphere. That venting will be assisted by an upper-level trough northeast of the storm and an upper-level low southwest of the storm (the same one that has been causing shear today). This upper-level pattern is a very strong indicator of potential for rapid intensification if the storm’s structure is organized enough to take advantage.

As the storm approaches the Louisiana coastline, it will start to encounter another obstacle: mid-level dry air and increasing westerly shear ahead of an upper-level trough.

Image via TropicalTidbits

Storm-centered cross sections on the HWRF model show the potential for some dry air intrusion as the storm nears the SE Louisiana coastline. It’s really hard to tell ahead of time how exactly the storm will interact with this type of dry air/shear. If its inner core is intense enough, it will barely notice this level of disruption (a la Laura). If the inner core is still struggling to get together, it could weaken quite a bit (Marco was an extreme example of this, though I wouldn’t expect that much weakening from Sally). I include this in here not to downplay the threat from Sally but to offer a little bit of hope that the door is still open to a lower-impact scenario. Prepare for the worst and hope for the best.

So what should residents of the northern Gulf Coast expect from Sally?

This map shows various key information from the NHC’s 5 PM update including the cone of uncertainty, projected wind radii, projected maximum wind speeds, rainfall, and watches/warnings. Note that dangerous impacts in the form of heavy rain extend well east of the center. So while landfall is expected in Louisiana, heavy rain (6-12+”) capable of major flooding issues will fall as far east as the Florida Panhandle. Storm surge of 1-3 feet is projected as far east as the Big Bend area of Florida. So while the landfall point and cone of uncertainty thereof get lots of attention, remember that even if you’re outside the cone and perhaps outside the worst of the winds, this may very well still be a dangerous storm for you.

Also note that Hurricane Watches are now posted for parts of southeastern Louisiana including New Orleans as well as southern Mississippi and southern Alabama. The time to start preparing for hurricane conditions in these areas is now.

Image via TropicalTidbits

As Sally approaches the northern Gulf Coast, it will slow down in response to a building ridge over the Plains. It may only be moving 3-5 mph, about as fast as most people can walk/run, when it makes landfall. This means that the system’s winds will have additional time to pile storm surge into the coast and heavy rain will linger over the same areas for quite a while. The net result, particularly if the storm does end up moving quite slowly, is an amplification of water-related threats.

The system will move inland sometime during the middle of next week. Heavy rains will continue for a while inland, but because the storm is moving so slowly, intense winds are not expected to continue inland like they did with Laura.

If you’re currently under a Hurricane Watch, begin preparations for Sally now. Always heed the advice of local officials and consult with official NHC/NWS forecast information when making any decisions that involve the protection of life and/or property.


Tropical Depression Nineteen Slowly Organizing Near Southern Florida This Morning

Hello everyone!

This is your morning briefing on Tropical Depression Nineteen which is the system in the Atlantic most likely to bring significant direct impacts to the US over the next several days. Of course there are several other systems worth watching (Paulette if you’re in Bermuda, 95L if you’re in the NE Antilles) but there’s not much new to say about those systems this morning, so they will be the subject of future updates.

Imagery via COD SATRAD

One of the GOES-East instruments capable of capturing satellite imagery every 60 seconds is pointed towards TD-19 this morning which gives us a helpful look at the system’s organization. There have been several bursts of impressive deep convection associated with the system this morning, though they’ve all been south or southeast of the storm’s low-level center. How can we find the low-level center? Once the sun comes up you can use visible satellite imagery, but radar imagery and surface observations are a bit more reliable so let’s use those.

In white, I’ve highlighted some surface wind direction observations as well as the low-level swirl you’d see if you looked at a radar loop. Note that all the heavy rain (>40 dBZ) is south and east of the low-level center. While last night there was one cluster of thunderstorms making a convincing case to be the low-level center, that’s no longer the case this morning with a few different swirls drifting through the Florida Straits.

So what happens next? I see three general possibilities. The first is that deep convection redevelops over the low-level center once it moves offshore later this morning. This is pretty much the going NHC forecast, and it’s definitely possible. This would lead to TD-19 strengthening and becoming TS Sally by this afternoon. The second possibility is that the initial low-level center dies off and a new low-level center forms under one of those convective bursts to the south. This would also support strengthening later today, though it might take a little bit longer. The third possibility is that the initial low-level center remains dominant but doesn’t get any deep convection. That would lead to a much weaker system, at least for the next 12-24 hours.

Unfortunately, it’s darn near impossible to say which of these possibilities will occur. I’d put the odds somewhere near 45%-45%-10% for scenarios 1-2-3. There really isn’t much shear over the storm, and the shear that is around will be fading later today so I don’t see this vortex misalignment persisting for much more than the next 6-12 hours.

By tonight/tomorrow morning, the system will be over the Gulf of Mexico and gaining a bit of separation from Florida. It should then begin intensifying thanks to a favorable environment including very warm water, relatively low wind shear, and high mid-level moisture. If you want a more complete breakdown of TD-19’s environment, please refer to last night’s post.

This graphic shows some key information from the NHC’s 5 AM advisory along with a couple notes from me. The system did indeed job farther southwest than was originally expected, though note that this morning’s center fix is still within the cones of uncertainty from yesterday. So it’s not that big of a surprise. This has nudged the storm’s expected track a hair west over the next 24-48 hours. As a result, the system might have a little more time over water and “room to breathe” as it moves NW towards the SE LA/S MS/S AL area early next week.

The intensity forecast for the system remains mostly unchanged from last night. TD-19 should approach the coastline as a strong TS or low-end hurricane, though there’s some uncertainty regarding its exact intensity because we don’t know how quickly it will organize in the next 24 hours. I wouldn’t be surprised to see future updates show an increase in forecast intensity if the storm can consolidate today around a single low/mid level center under some persistent deep convection.

Tropical Storm watches are now posted for parts of the Florida Panhandle and will almost certainly be expanded westward towards SE LA later today. Residents in this area should be paying close attention to forecasts and should have their hurricane plans ready to implement if/when watches go up and local officials begin issuing guidance about how to prepare for the storm.

I’ll be back later today with more updates both here and on the HurricaneTrack Patreon page.


Tropical Depression Nineteen Forms East Of Florida, Likely To Approach Hurricane Strength Before Landfall On The Northern Gulf Coast Next Week

Hello everyone!

It’s an extremely busy day in the tropics as we have six systems to watch from the Gulf of Mexico to the shores of western Africa.

Imagery via NESDIS STAR

Each of these systems can be seen on this satellite image of the Atlantic a little earlier this afternoon. In order from west to east: the trough over the NW Gulf with a 30% chance of development within five days, TD-19, Paulette, Rene, 95L, and the next wave just emerging off Africa.

This post will start with a quick look at Paulette before taking a deep dive into TD-19’s forecast. None of the other systems will be mentioned due to their relatively low threat to land (zero for Rene, unclear long-term threat for 95L, minor longer term threat from the GOM trough, and potential for showers in Cabo Verde from the next wave) and the presence of more pressing systems.

Before we really dive into this evening’s update, a couple notes. If images are too small for you to get a good look at, you can click them for a larger version. If you’d like to get these updates in your inbox, you can sign up with the box on the left sidebar near the top of the page. If you’d like to see more tropical weather updates from me while supporting a super cool hurricane research project, head on over to Mark Sudduth’s Patreon page. If you prefer to support me directly, I also have a personal Patreon page. It’s like Mark’s except without all the cool extra posts and the money goes to buying my textbooks instead of collecting data from inside hurricanes.


Imagery via NESDIS STAR

The strongest system in the Atlantic this evening is Paulette with winds of 65 mph. The storm is expected to become a hurricane tonight or tomorrow as it continues tracking northwest towards Bermuda. Significant impacts from Paulette are likely in Bermuda as the storm passes nearby on Monday morning. Just how close to the island the storm gets will determine the extent to which rain/wind/surge will cause problems there. If you’re looking for more of my thoughts on Paulette and Bermuda, I took a bit of a closer look in my post this afternoon for Mark Sudduth’s page.

For those of us along the East Coast, Paulette is nothing to worry about outside of concerns relating to large swells and rip currents. If you’re an experienced surfer, by all means enjoy the powerful swells. For the rest of us, stay out of exposed ocean waters where intense rip currents pose a serious threat to your life.


TD-19 was just designated east of Florida from the system we’ve been calling 96L up until today.

Imagery via RAMMB SLIDER

Satellite imagery shows an increasingly healthy system this evening with fairly expansive upper-level outflow (still needs to work on the northwestern quadrant and intense thunderstorm activity bubbling up near the system’s center (especially towards the end of the loop). Those persistent bursts of thunderstorm activity over the center will be key for the system’s development over the next few days. If thunderstorm activity continues tonight the way it has been this afternoon, I honestly wouldn’t be shocked to see TD 19 upgraded to TS Sally by the 8 PM or 11 PM EDT updates.

TD-19 is close enough to the Miami radar that we can actually get some pretty good information about the system’s structure by peering under the cirrus canopy and into the lower-level parts of the storm. The mid-level circulation is located in the cluster of intense thunderstorms just off Andros Island while the lower-level center (lowest surface pressures inferred by observations in Florida and buoys/ships offshore) is a bit northwest over the Florida Straits. This infers the presence of some light northwesterly wind shear which is preventing the system from becoming fully aligned.

That wind shear is being caused by a weak upper-level low drifting southwest across central Florida. As that low slides farther southwest, continues weakens, and the deep convection associated with TD 19 begins to produce a response in the lower-level mass fields (i.e. enough air rises in the big thunderstorms that more has to move horizontally towards the storm’s center to take its place), I’d expect to see this misalignment resolved. It also helps that the low-level center is somewhat poorly defined and doesn’t have much angular momentum built up yet so a center relocation underneath that deep convection is pretty easy for a storm like this to pull off.

Imagery via NRL

Microwave imagery from around 5 PM shows a system well-positioned for intensification with a curved band of convection developing around the mid-level center. Note that the convection hasn’t yet wrapped around to the northwest of the mid-level center, due in part to the wind shear mentioned above. If that band can close off, TD-19 could make a run towards mid-grade TS status before landfall tonight. That’s far from a guarantee given the NW shear, and it would only impact a few towns right along the beach where the very small core comes ashore, but it’s something to be mindful of if you live in the Miami area. Don’t be shocked if your power flicks off for a few hours tonight if TD-19 happens to tighten up a bit before landfall and you happen to end up in the small portion of the circulation that contains 40-50 mph winds.

After moving onshore tonight, TD-19 will quickly move across the southern part of the peninsula before emerging offshore tomorrow afternoon. The state of the system at this point is a bit of an unknown because we don’t know how robust the circulation will be when it moves onshore tonight and we don’t know to what extent the circulation will fall apart over land. We also don’t know how long the storm will spend over land because its exact track is a bit uncertain owing to near-term wobbles induced by the strong convection discussed earlier.

Data via tropicaltidbits

Either way, by tomorrow afternoon TD 19 will be offshore between Naples and Key West. At this point, it will begin to strengthen in an environment favorable for tropical cyclone development.

For tropical cyclones to develop and intensify, three main ingredients are needed: warm water, low vertical wind shear, and relatively high mid-level moisture. Sea surface temperatures are over 30C in the Gulf of Mexico at the moment (need ~26C for tropical storms, ~28C for hurricanes) so there’s nothing holding the storm back on that front. What about shear and dry air?

Data via tropicaltidbits

This area-averaged sounding over TD-19 tomorrow evening shows no dry air or wind shear in sight as the system sits within a very moist environment characterized by nearly uniform east-southeasterly winds between 5 and 10 kts. This basically means that there’s very little if anything holding TD-19 back as it moves into the eastern Gulf on Sunday.

Data via tropicaltidbits

As a result, it’s not surprising to see the models that are designed to offer more accurate intensity forecasts for tropical cyclones bring TD-19 quickly up to a strong TS by Monday. The animation above shows the HWRF which shows TD-19 coming very close to landfall in AL as a category one hurricane by Monday night. Much like other storms this season (Hanna, Isaias, arguably Laura), the biggest cap on TD-19’s intensity will be its limited time over water.

With that in mind, generally speaking if TD-19 wobbles south tonight/tomorrow or winds up tracking farther SW on Sunday, it will have more time over water and will thus have more time to intensify.

Now that we understand the rough contours of TD-19’s forecast including what factors will influence its intensity, its a good time to present the NHC’s forecast for not just the storm’s track (cone of uncertainty + “most likely” centerline forecast) but also its size. Note that the system starts out relatively small but quickly expands as it approaches the northern Gulf Coast. This means that, as per usual with tropical cyclones, impacts will extend well beyond where the actual center makes landfall. So even though we still don’t know where exactly the center will move onshore (SE LA or FL Panhandle or anywhere in between), folks along this part of the Gulf Coast should start getting their hurricane plan ready tonight/tomorrow in anticipation of needing to take actions Sunday or Monday.

As the storm approaches the northern Gulf Coast on Monday, it will slow down and turn towards the west in response to a bit of a collapse in steering currents.

Data via tropicaltidbits

This area-averaged sounding from the GFS valid Monday morning shows very little environmental steering flow over the system, aside from some very weak (~5kt) east-southeasterlies in the lower levels of the atmosphere. What impacts might this have on TD-19 and the weather for W FL/S AL/S MS/SE LA?

The first noteworthy impact will be an increase in the heavy rain threat. Slow-moving tropical cyclones, as this looks to be, are notorious for producing very heavy rainfall. Even if the storm doesn’t become a hurricane, it will produce very heavy rain that will cause flooding problems even in places well away from the center. So if your location is prone to flooding and you’re anywhere between Tallahassee Florida and Lafayette Louisiana, you should start thinking about what actions you might need to take should high water become an issue. Hopefully you already have a plan in place so that if/when watches and warnings are issued by your local NWS office, you’re ready to act in a timely manner.

The other impact of the storm’s slower forward motion near landfall might be a bit of a reduction in the wind threat. Tropical cyclones, especially if they’re strong, churn up the waters beneath them. When a cyclone is over shallow water, it’s able to mix up cooler water from below the surface a bit easier than if the cyclone is moving over a deep reserve of warm water. So I could see TD-19 intensifying into a hurricane on Sunday night before fading a little bit in the last few hours drifting into landfall. Note that this isn’t a guarantee, and you should not plan on this last-minute weakening, but it’s something to keep an eye out for as we watch the storm’s track forecast shift around a bit in the coming days.

Eastern Atlantic Systems

Out in the eastern Atlantic, we’re still keeping a half an eye on Rene, 95L, and the next wave sliding off Africa. Rene poses absolutely zero threat to any landmass, the next wave might bring some breezy showers to the Cabo Verde Islands, and 95L is the one to watch for potential development into a long-track hurricane next week.

Map via

That said, ensemble guidance is still so inconclusive regarding the future of 95L past three or four days that there’s no point speculating much about what potential impacts might look like in the Caribbean or elsewhere. If you’re in Puerto Rico or the northeastern Lesser Antilles, keep a close eye on this system in case it becomes more of a threat this weekend/early next week. For the rest of us, we have plenty to focus on with TD-19 for the next four or five days until guidance gets a better handle on 95L.

More updates tomorrow and in the days to come. If you’d like to see these updates in your inbox the moment they are published, feel free to sign up using the sidebar to the left (near the top of the page).


Watching Paulette, Rene, and Four Disturbances in the Atlantic

Hello everyone!

Today, September 10th, marks the official climatological peak of hurricane season, though activity doesn’t usually start subsiding until later in October. Given the time of year and all the conditions both seasonal and subseasonal that are favorable for enhanced tropical cyclone activity, it’s no surprise we have so much to keep an eye on in the Atlantic.

This post will take a fairly deep dive into the forecasts for Paulette and the two disturbances in the Gulf of Mexico. Rene poses no threat to any landmass and thus won’t be covered. I’ll also mention the next waves coming off Africa, though there’s so much near-term uncertainty regarding how those entities interact that I’m not going to spend much time trying to explore the medium-term range of possible outcomes which spans from a hurricane in the Caribbean to a tropical storm dissipating over the far eastern Atlantic. I’ll revisit these waves on Saturday once we have a better idea of how they’re developing offshore.

TS Paulette

Imagery via NOAA NESDIS

Satellite imagery today shows Paulette struggling significantly with dry air and wind shear attributable to an upper-level low located west of the system. Note on this “sandwich” satellite imagery that the low-level center visible as the swirl of low clouds in white is located south/southwest of the mid-level center and its associated deep convection which is visible as the red blob indicating very cold cloud temperatures. So long as the storm remains misaligned like this, it will not be able to strengthen, and in fact will continue to weaken.

Data via TropicalTidbits

This area-averaged sounding over Paulette valid tomorrow evening shows dry air and southwesterly shear continuing to impact the system as it continues moving NW. The benefit of looking at an area-averaged sounding like this is that the system’s circulation disappears (average the winds across a circular circulation and you get net zero) which allows us to peer into the system’s environmental wind field. From this, we can clearly see the southwesterly shear vector arising from a difference between low-level easterlies and mid/upper-level southerlies/south-southwesterlies.

Aside from attempting to separate Paulette’s low-level center form its mid-level center, this change in wind direction with height also has implications for the system’s track forecast. If the storm is able to retain really robust convection and maintain a deeper (albeit tilted) vortex, it will “feel” the steering influence of those upper-level southerlies. That means the storm will track farther north. If the system weakens and has a shallower vortex, it will be steered mostly by the low-level easterlies. As a result, a stronger Paulette tonight/tomorrow will wind up farther north by Saturday while a weaker Paulette will stay farther south.

Data via TropicalTidbits

By Sunday, Paulette will begin restrengthening and will make a turn to the west as upper-level flow shifts from southwesterly to easterly. This shift will be driven by the southwestward movement of the ULL currently shearing the system as well as the development of an upper-level ridge off the New England coastline. Note that on the area-averaged sounding over the circulation Sunday morning, winds throughout the atmosphere are out of the east at around 10-15 kts. This lack of change in wind speed or direction with height is the lack of shear that tropical storms need to strengthen.

So how long will the storm move west and how close to the US East Coast will it track? By Monday, the storm will turn towards the north, away from the East Coast. Whether this happens 500 miles offshore, as currently forecast, or 300 miles, or 800 miles, it’s not exactly clear. But I’m quite confident that this is not a system headed close enough to the East Coast to bring substantial direct impacts. Why?

Data via TropicalTidbits

This forecast map shows the upper-level pattern on Monday afternoon. There are three main features contributing to Paulette’s steering flow at this point: the upper-level low that previously had been steering the storm west, a new mid-latitude trough digging southeast through the Canadian Maritimes, and an upper-level low developing over eastern Florida. All of these features will be pushing Paulette north-northeast. If there were a big area of high pressure where that mid-latitude trough is located, I’d say watch out along the East Coast. But the pattern simply isn’t set up to allow those big ridges to hang out off the New England coast. Why not? Typhoon Haishen basically “undid” the jet stream amplification that Typhoon Maysak caused last week. So instead of a very wavy jet stream with slow-moving troughs and ridges, we have a flatter jet stream with features moving relatively quickly from west to east.

With that in mind, despite considerable uncertainty regarding how far west Paulette goes in the next 72 hours, not a single EPS ensemble member brings the system close enough to bring substantial direct impacts to the US East Coast. If you’re in Atlantic Canada, especially Newfoundland, you should keep a close eye on Paulette. Bermuda is the most likely landmass to see substantial direct impacts from Paulette as the storm turns north on Monday.

Imagery via

While rain/wind/storm surge is not expected along the East Coast from Paulette, the shoreline will still take a beating from the system in the form of powerful long-period swells. This animation shows forecasts for “wave power” over the next week as Paulette restrengthens and recurves off the East Coast. These swells will cause dangerous conditions for mariners as well as large breaking waves at exposed locations along the shoreline. If you’re an experienced surfer, enjoy the sweet waves. For everyone else, be mindful of the high rip current risk these waves will pose at beaches exposed to the ocean.

Gulf of Mexico Disturbances

Elsewhere in the Atlantic, we have two disturbances to keep an eye on for possible development in the Gulf of Mexico late this weekend into early next week.

Data via

This satellite loop shows one of those disturbances which is currently located just east of the Bahamas. The system is producing a lot of convection this afternoon which is impressive because this is the time of day least favorable for convection over tropical waters. That’s one sign that this disturbance is healthy. Another sign is that cirrus clouds produced by these thunderstorms are fanning out away from the system in an anticyclonic pattern, especially over the eastern half of the disturbance. Note the cirrus moving north to the north of the system, to the west on the southern side of the system, and east on the eastern side of the system. This indicates an upper-level environment favorable for further development.

The other disturbance is producing scattered thunderstorm activity just off the west coast of Florida this evening, but doesn’t look like much on satellite imagery.

Data via

By Sunday morning, both systems will be in the Gulf of Mexico. Looking at forecast guidance for this timeframe, it’s clear why model guidance and NHC forecasters are significantly more bullish on the eastern system. There’s a whole lot more moisture and instability available for that system to work with compared to the western system.

That said, any time you get a disturbance spinning over the very warm waters of the Gulf of Mexico, it doesn’t take much for deep convection to develop and mix out any mid-level dry air, especially without any wind shear (there won’t be much if any shear in the Gulf this weekend). So we’ll keep an eye on both systems, even though I think the eastern one has a much better shot at becoming a tropical cyclone.

Data via

Here’s a look at afternoon ECMWF ensemble guidance for these systems. Note that pretty much no ensemble members develop the western disturbance beyond a brief TD. The range of possible outcomes for the eastern wave as depicted by the EPS ranges from no development at all to a mid-grade tropical storm. Given the favorable conditions expected in this area, my personal “upper limit” of what seems plausible from this system is a bit higher (perhaps in the strong tropical storm range).

If you’re in southern Florida, you should expect periods of breezy showers as this system passes by tomorrow. If you’re in Louisiana, Mississippi, Alabama, or the Florida Panhandle, you should be paying attention to forecasts in case this system turns out to be something worth thinking more about.

Eastern Atlantic Systems

Out in the eastern Atlantic, there are two additional systems to keep an eye on for tropical development over the next few days. Both are clearly visible on satellite imagery this afternoon.

Data via

The central question regarding these systems is the extent to which they will interact over the next 24-48 hours. One possibility is that the western wave will move quickly west as its center develops under that northern lobe of convection south of the Cabo Verde islands. If that ends up happening, and the eastern wave moves offshore a little slower, the two systems will remain separate and we could see two named storms develop this weekend. Another possibility is that the western wave ends up consolidating its center farther west, moves more slowly, and interacts more significantly with the eastern wave. If that ends up happening, we may only get one storm to develop in this area.

Data via

A look at ensemble member forecasts for the next few days show two distinct “camps” representing each of the possibilities outlined above. Generally speaking, the ensemble members in the “fast and separate” camp are more threatening for interests in the Lesser Antilles, and eventually the Greater Antilles/US much later down the line. Ensemble members that show more interaction and an overall slower storm motion are substantially more likely to show the system recurving off into the open Atlantic like Rene and Paulette.

Which scenario is more likely? I’m not quite sure at the moment because the problem of “which vortmax will become dominant” is really hard to solve due to its dependence on nearly-random convective interactions. Once both waves are offshore late tomorrow/Saturday, I suspect we’ll have a much better idea of what will happen.

Until then, monitor forecast info closely and make sure your hurricane plan is ready to go if you’re reading from the Lesser Antilles. If you’re reading from anywhere northwest of Puerto Rico, check back in on Saturday to see what’s up and until then, don’t worry too much about these systems. There’s still plenty of time to watch and wait, painful as that may be.

As a reminder, if you’re interested in having my weather updates emailed to you, you can sign up using the box on the left sidebar of this website. If you’re interested in having my updates on an app for your phone, please search for the “Hurricane Tracker App” in the app store. If you’re interested in reading my tropical weather analysis while supporting a super cool crowdfunded hurricane research project, check out Mark Sudduth’s HurricaneTrack Patreon page.


An Introduction to

Hello everyone!

This week has been full of exciting new developments for me as I move into the next chapter of life as a weather forecaster and aspiring meteorologist. After moving on from a very fulfilling several years at, I’m now working on a few different projects to keep folks informed as hurricane season ticks on.

You can find my updates on your phone with the Hurricane Tracker App, and on Patreon with Mark Sudduth’s HurricaneTrack project.

So why am I opening up another platform here? One reason is that I’ve gotten some questions inquiring about signing up for my updates via email. The option to have updates emailed to you is one that folks following my ME/NH weather blog seem to have appreciated over the years, and this platform will allow for that capability.

Additionally, my other projects each have a specific audience/ purpose/topic area focus. Info posted on the Hurricane Tracker App is aimed at a more general audience interested in quick updates. Info posted on Mark Sudduth’s page is intended for deeper dives “behind the scenes” to support Mark’s work chasing down and documenting landfalling storms. This page will be a catch-all for commentary and updates about weather not just in the tropics but wherever interesting stuff is happening. 

So if you’re interested in a “classic” blog interface with the option to sign up for updates via email, this is the spot. If you’re interested in a slick mobile interface with updates that are more concise, Hurricane Tracker App is the place to go. If you’re interested in some more behind-the-scenes stuff in support of a really cool hurricane science project, head on over to Mark Sudduth’s page.

Hopefully you will find my updates interesting and informative during periods of active tropical weather and when things are quieter. As always, feel free to reach out with any questions you may have about the weather. I’ll do my very best to get back to you!