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GaWx

Tropical Atlantic 2015 speculation/action

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Decent, potentially sustained flareup on convection across the NW quadrant of Invest 98L this afternoon.  Wouldn't be surprised if we see TD #5 at the 5:00 pm advisory.

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Not sure why the avoidance of declaration given 18z initialization? Seems like we've had a lot of straight from invest to TS in one advisory and just skip the TD stage in the Atlantic basin.

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Not sure why the avoidance of declaration given 18z initialization? Seems like we've had a lot of straight from invest to TS in one advisory and just skip the TD stage in the Atlantic basin.

The only thing I can guess is that they are waiting for it to pass that one buoy, but that's a bit anal

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Classification as a TS won't change the impacts to the Lesser Antilles, which will be the same whether the system is Erika or a low pressure area along a sharp trough axis. I wouldn't upgrade something on the basis of ambiguous evidence, as ASCAT showed a very elongated circulation that arguably wasn't closed. Furthermore, 98L has failed to generate convection sufficiently close to its alleged center for an upgrade. Additionally, 98L will face even worse conditions beginning in another day, so if it's struggling now (thanks to easterly shear in the mid to upper levels, plus stable air to its north), it will really struggle against the TUTT near the islands, no matter how broad a system it is. I wouldn't waste an upgrade on something that may not even develop and certainly, in my view, won't evolve beyond a minimal tropical storm (40-45 kt) at most. If someone disagrees with me and the global models (ECMWF especially, but also GFS), then I'd like to hear the reasoning.

 

 

But that's not a reason to hold off. EPAC storms go right to TD too. Seems like the Atlantic basin is the one going from invest to TS. What happens to the storm in the future is irrelevant when it comes to the science. That is not a reason to hold off even if true.

I didn't disagree about the science; I mentioned the fact that ASCAT and satellite data seemed insufficient to upgrade.

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But that's not a reason to hold off. EPAC storms go right to TD too. Seems like the Atlantic basin is the one going from invest to TS. What happens to the storm in the future is irrelevant when it comes to the science. That is not a reason to hold off even if true.

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Classification as a TS won't change the impacts to the Lesser Antilles, which will be the same whether the system is Erika or a low pressure area along a sharp trough axis. I wouldn't upgrade something on the basis of ambiguous evidence, as ASCAT showed a very elongated circulation that arguably wasn't closed. Furthermore, 98L has failed to generate convection sufficiently close to its alleged center for an upgrade. Additionally, 98L will face even worse conditions beginning in another day, so if it's struggling now (thanks to easterly shear in the mid to upper levels, plus stable air to its north), it will really struggle against the TUTT near the islands, no matter how broad a system it is. I wouldn't waste an upgrade on something that may not even develop and certainly, in my view, won't evolve beyond a minimal tropical storm (40-45 kt) at most. If someone disagrees with me and the global models (ECMWF especially, but also GFS), then I'd like to hear the reasoning.

I didn't disagree about the science; I mentioned the fact that ASCAT and satellite data seemed insufficient to upgrade.

It's a tough call as to whether or not the circulation is closed right now. The buoy it just passed near didn't record much if any westerly wind and it was open this morning during the ASCAT pass. I do disagree that 98L has "failed to produce convection sufficiently close to" its center, as late day visible, current shortwave IR imagery and microwave imagery show that although the center isn't directly under the strongest convection, it is near the northern edge of it. I think the only hold up on designation now is questions over whether or not the low is closed, because the convection is robust enough and close enough to the center for an upgrade if they deem the center to be closed. The NHC has been very conservative on designating systems if they aren't sure the center isn't 100% closed over the last several years it seems.

I'm not optimistic on future prospects for this system but that does not preclude an upgrade if evidence of a closed circulation emerges. The global models show about 36-48 hours before the invest moves into increasing shear due to the TUTT axis, with favorable outflow before then. Considering that the system is already close to classifiable and producing gale force winds, I'm fairly confident in this developing into a TS before it begins to get sheared too strongly. Given the large and not very organized nature of the system right now, rapid intensification to anything more than a low to moderate end TS is probably unlikely. Unless this system can become stronger within the next 48 hours it could well suffer a similar fate as Danny. The Euro appears to get the remnants north of Hispaniola/Cuba and has an OK looking environment over the Bahamas should the entity survive that long although the 12z GFS appears to track the remnants over the spine of Cuba and is less optimistic about weakening shear near the system later. If the system manages to get sufficiently deep within the next 48 hours, its larger size and stronger UL anti-cyclone could help mitigate the shear's impact some and also pull it north of the Greater Antilles (ala the Canadian)...given the current organization of the invest and limited time for that to happen I'm leaning against that happening...but I think we'll still probably get Erika out of the deal.

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Winds turned to the S and SSW pretty abruptly at that bouy, with a little over 30 kts sustained for about and hour and gusts to near 40 out of the SSW.  I agree with some of the above comments about the NHC being sticklers on a W wind, closed circulation before classification.  The one thing that it may have going for it that Danny didn't is it's size and there's not nearly as much dry air in the vicinity.  more important from the CIMMS wind analysis, it's anticyclone is fairly strong and is well centered above.  It's a wait and see on the TUTT, although well established recently, it has waned.  I think the key is going to be the upper high above 98l and how well they can stay aligned.  Like most of these storms it's all about timing I guess.

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This ASCAT did it...

 

...TROPICAL STORM FORMS OVER THE CENTRAL TROPICAL ATLANTIC...

ascat2515082502_98_INVEST_as.png

 

 

Satellite imagery, buoy observations, and a very recent ASCAT pass
suggest that the circulation associated with the area of low
pressure over the tropical Atlantic has become better defined.
Deep convection also became better organized during the afternoon
and has persisted in a band over the southeastern portion of the
circulation this evening. The NOAA buoy reported peak south-
southwesterly winds of 39 kt, and a minimum pressure of 1004 mb.
Based on these data, advisories are being initiated on a 40-kt
tropical storm. Erika becomes the 5th tropical storm of the 2015
Atlantic hurricane season.

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NHC track would seem to suggest big Florida threat.

 

 

If it doesn't get sheared to pieces first.

I know the horse left the barn on this issue some time ago, but this is why I think the forecasts should be limited to 72 hours, especially for nascent systems. 

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I know the horse left the barn on this issue some time ago, but this is why I think the forecasts should be limited to 72 hours, especially for nascent systems. 

 

5-day track/intensity and genesis forecasts are customer-driven. Besides, there's no way on earth you'd ever get anyone, be it a professional or an armchair forecaster, to not speculate beyond three days. As long as the proper caveats about uncertainty are given (which they are), the state of the science allows for forecasts out to 5 days.

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The negativity here is pretty astounding. It was just classified and some are dismissing it already.

Eh, across all wx types now there is a "coolest guy in the room" element where people compete to downplay a system more than the next guy; if you can write a post with the most bored and dismissive tone,it's a victory. It's more prevalent NOW than rampant OMIGOD ITS THE NEXT ANDREW!!! Weenie-ism. Of course you more likely to happen to be right doing the former than the latter, whether it's a tropical system, a modeled tornado outbreak, or a blizzard.

That said, let's see how they field the massive Erika bomb off Georgia on the EC from today. should be fun.post-986-0-49445500-1440502587_thumb.jpg

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Does anyone know why the August-September TUTT has been so persistent since 2010? I found a study indicating that climate change could, in part, contribute to stronger vertical shear near the Caribbean islands thanks to a more persistent TUTT. Of course, there is plenty of seasonal variability, but I would like to know if the TUTT will finally be less prevalent next season during prime time. Otherwise, systems forming in the MDR would likely struggle near the Lesser Antilles.

 

HUOsENb.png

 

Additionally, one thing's clear: if the CFS forecast for a large Atlantic warm pool for next year verifies into the heart of the 2016 season, we may see even fewer opportunities for U.S. landfalls, at least with MDR storms. According to this study, a strong AWP correlates with a weaker Bermuda High, allowing for more MDR development, but also more opportunities for those storms to miss the U.S. So we could go another season without major landfalls.

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Onto Invest 99L...

 

pdEV2jT.png

ZCZC MIATWOAT ALL
TTAA00 KNHC DDHHMM

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT SAT AUG 29 2015

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical
Storm Erika, located near eastern Cuba.

1. Showers and thunderstorms are gradually becoming better organized
near a low pressure area located just off the coast of Africa about
150 miles west of Conakry, Guinea.  Environmental conditions are
expected to be conducive for development during the next few days,
and a tropical depression could form while the system moves
northwestward and then west-northwestward toward the Cape Verde
Islands at 10 to 15 mph.
* Formation chance through 48 hours...medium...50 percent
* Formation chance through 5 days...high...70 percent

Forecaster Berg

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