Tag Archives: Rene

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 weathernerds.org

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 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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