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Atlantic Tropical Action 2014


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The system behind 93L actually looks a lot more organized...I'm surprised that it isn't an INVEST yet (not that I think it will develop into anything of significance). Several models briefly develop a closed low that loses identity in three days. Also, the environment surrounding it will be more moist than what 93L is moving through. And the system currently has much more convective organization than 93L does.

 

For some reason, the HWRF and the GFDL have been consistently forecasting 93L to be near hurricane intensity by August 1. The 12Z HWRF (and to a lesser extent the 06Z GFDL) also shows 93L developing robust convection within 24 hours. What in the convective parameterization is causing these models to miss the robust SAL / low RH surrounding 93L? Such an error in short-range forecasting would be quite bad.

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The system behind 93L actually looks a lot more organized...I'm surprised that it isn't an INVEST yet (not that I think it will develop into anything of significance). Several models briefly develop a closed low that loses identity in three days. Also, the environment surrounding it will be more moist than what 93L is moving through. And the system currently has much more convective organization than 93L does.

The 12z GFS intensifies this system for the next two days before it falls apart.

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For some reason, the HWRF and the GFDL have been consistently forecasting 93L to be near hurricane intensity by August 1. The 12Z HWRF (and to a lesser extent the 06Z GFDL) also shows 93L developing robust convection within 24 hours. What in the convective parameterization is causing these models to miss the robust SAL / low RH surrounding 93L? Such an error in short-range forecasting would be quite bad.

 

The HWRF is of sufficient horizontal resolution that it does not need a convective parameterization. While there might be other deficiencies in the model physics itself (e.g microphysics) you can't blame this on the convective scheme here. The more problematic thing here is that (as far as I am aware of) most meteorological dynamical models forecasts currently don't really account for aerosols. Thus, the GFS, ECMWF, HWRF ect. don't actually know the SAL is there (other than if its possibly accounted for by IC radiances from POES or GOES). 

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000
ABNT20 KNHC 301734
TWOAT

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT WED JUL 30 2014

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

Showers and thunderstorms associated with an area of low pressure
located about 1000 miles east of the southern Windward Islands have
been gradually decreasing since yesterday. However, environmental
conditions are marginally conducive for the development of this
system into a tropical depression during the next couple of days.
Interests in the Lesser Antilles should monitor the progress of this
system as it moves west-northwestward near 15 mph.
* Formation chance through 48 hours...medium...50 percent.
* Formation chance through 5 days...medium...50 percent.

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The dry and more stable air over the Tropical Atlantic has resulted in a very impressive

tropical cyclone statistic. From the beginning of the 2011 hurricane season through

today there have been 51 named storms in the Atlantic Basin. Only 2 storms

were able to reach hurricane status while in this region since then. Both Humberto

in 2013 and Katia in 2011 only made it to category 1 strength in this box. The

last major hurricanes occurred back in 2010.

 

 

 
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What is the cause of the increase in the SAL over the past few (couple?) of years?

*sarcasm* Anything other than climate change…which is a topic for another thread. *sarcasm*

 

In all seriousness, a more direct cause is the Sahel drought and a shift in the Hadley circulation over the Atlantic. The PDO explanation doesn't really make sense given that previous -PDO cycles coincided with high precipitation in the MDR. Interestingly, although the Indian Ocean has cooled off over the past month, we're still having serious problems with lower-than-average instability. I also can't recall the last time I've seen 26-27° C SSTs so far south and west in the MDR this time of year. That's frigid by climatological standards.

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This is probably at least a TD. Convection has returned near the center, and although it's sheared by westerlies, ASCAT shows that it's a vigorous closed low now. Strength maybe very close to 35kts if one takes into account there's a relatively large area of 30kts wind barbs and ASCAT's underestimating bias.

 

post-29-0-33828800-1406774304_thumb.png

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This is probably at least a TD. Convection has returned near the center, and although it's sheared by westerlies, ASCAT shows that it's a vigorous closed low now. Strength maybe very close to 35kts if one takes into account there's a relatively large area of 30kts wind barbs and ASCAT's underestimating bias.

 

attachicon.gifWMBas100.png

But with the dry air around, the convection will likely fade by tomorrow morning. I wouldn't call it a TD or TS unless convection were to persist as per NHC criteria. SSTA are warmer near the islands, but the system will have its moisture source from the ITCZ cut off as it tracks to the west-northwest. While some of the dry air has mixed out over the past several hours, another trade surge of dry SAL is also approaching from the east. At this point I'm not optimistic, even though the GFDL and the HWRF have raised their intensity estimates over the next two days.

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But with the dry air around, the convection will likely fade by tomorrow morning. I wouldn't call it a TD or TS unless convection were to persist as per NHC criteria. SSTA are warmer near the islands, but the system will have its moisture source from the ITCZ cut off as it tracks to the west-northwest. While some of the dry air has mixed out over the past several hours, another trade surge of dry SAL is also approaching from the east. At this point I'm not optimistic, even though the GFDL and the HWRF have raised their intensity estimates over the next two days.

Shear is going to diminish to ~10 kts for the next 24 hours. Thermodynamics are mediocre at best, but it will only take a slight organization improvement...or even status quo for a few hours to get numbered.

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Shear is going to diminish to ~10 kts for the next 24 hours. Thermodynamics are mediocre at best, but it will only take a slight organization improvement...or even status quo for a few hours to get numbered.

Compleatly agree, now that the convection has returned the shear still isn't prohibably strong to prevent TCG. As long as the convection doesn't wane, this should get to TD/TS even if the organization from here on out remains stagnant.

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Up to 70% now. Disco sounds like they may upgrade this later this morning :

TROPICAL WEATHER OUTLOOKNWS NATIONAL HURRICANE CENTER MIAMI FL800 AM EDT THU JUL 31 2014For the North Atlantic...Caribbean Sea and the Gulf of Mexico:A well-defined low pressure system located about 650 miles east ofthe southern Windward Islands has been producing organized showerand thunderstorm activity during the past several hours.  If thisactivity persists, tropical depression or tropical storm advisorieswill be initiated later this morning.   Interests in the LesserAntilles should monitor the progress of this disturbance as it moveswest-northwestward at 15 to 20 mph, and watches or warnings may berequired for some of these islands later today.  A HurricaneHunter aircraft is scheduled to investigate the system thisafternoon.* Formation chance through 48 hours...high...70 percent.* Formation chance through 5 days...high...70 percent.$$Forecaster Pasch
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Up to 70% now. Disco sounds like they may upgrade this later this morning :

TROPICAL WEATHER OUTLOOKNWS NATIONAL HURRICANE CENTER MIAMI FL800 AM EDT THU JUL 31 2014For the North Atlantic...Caribbean Sea and the Gulf of Mexico:A well-defined low pressure system located about 650 miles east ofthe southern Windward Islands has been producing organized showerand thunderstorm activity during the past several hours.  If thisactivity persists, tropical depression or tropical storm advisorieswill be initiated later this morning.   Interests in the LesserAntilles should monitor the progress of this disturbance as it moveswest-northwestward at 15 to 20 mph, and watches or warnings may berequired for some of these islands later today.  A HurricaneHunter aircraft is scheduled to investigate the system thisafternoon.* Formation chance through 48 hours...high...70 percent.* Formation chance through 5 days...high...70 percent.$$Forecaster Pasch

Given the dry air around it, and that it will be entering an area of high shear soon, I cannot see this system lasting very long, if it does make it to TD/TS status.

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I suspect RECON will not fly today unless there is a dramatic increase in convection N of the exposed center of circulation which is clearly visible this morning. This may have been a TD about 48 hours ago, but the future certainly does not look good for a viable tropical cyclone out of this swirl.

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I suspect RECON will not fly today unless there is a dramatic increase in convection N of the exposed center of circulation which is clearly visible this morning. This may have been a TD about 48 hours ago, but the future certainly does not look good for a viable tropical cyclone out of this swirl.

The visible loop tells the story. Looking at the IR loop it's not 100% clear if the center is fully exposed or just on the northern edge of the deepest convection.

 

rb_lalo-animated.gif

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Looks like a big convective blowup just south of the center currently

 

 

A cell 50 miles or so SSW of the LLC isn't enough to warrant an upgrade. We would need to see storms concentrated much closure to the center of circulation before any real chance of 93L developing any further. The exposed center is racing rather quickly to the W/WNW as well and that  should inhibit much more in the way of development. Look further E across Africa as we enter the month of August. There is some increase in convection along and N 10 that may weaken the  SAL a bit as we move along. We still have a lot of season left.vis-animated.gif

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