Tag Archives: tropical waves

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

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 surf-forecast.com

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 weathernerds.org

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 weathernerds.org

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 weathernerds.org

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 weathernerds.org

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 weathernerds.org

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.

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-Jack