ATL: TROPICAL DEPRESSION ALEX - DISCUSSION

[ronjon]

My take is that the system is really large, its proximity to SA (with descending drier air), and its apparent attachment to the ITCZ trough will limit any significant development over the next couple of days. That said, the large upper level high and high TCP, could make rapid development a real possibility in the NW caribbean sea. What the system seems to lack is good vorticity. Perhaps this is what the models are forecasting - no rotation to spark a cyclone. As a reality check though, none of these models are really good at forecasting tropical cyclogenesis.

[wxman57]

New here, guys/gals. Be polite! LOL. I have meteorological background and look forward to great discussions. Enough of that. Here's my first post. It appears as though our blob is trying to develop a closed circulation. See image below.
http://rammb.cira.colostate.edu/product ... 0_SWHR.GIF

How is this image generated? This is satellite scatterometry, I guess? What satellite instruments are involved?

Note that as stated above, they make assumptions that a mid-level (700mb/10,000ft) circulation extends down to the surface. That's not necessarily the case here. Surface obs in the area do not indicate any LLC.

What concerns me is that we do have a moderate to strong wave moving westward beneath a predicted building upper high vs. into 40 kts of shear like 92L. I might give it a 40-50% shot at developing by Wed/Thu.

[x-y-no]

Thanks Hurakan ...

So:

Multi-Platform Tropical Cyclone Surface Wind Analysis

Currently, this product combines information from five data sources to create a mid-level (near 700 hPa) wind analysis using a variational approach described in Knaff and DeMaria (2006). The resulting mid-level winds are then adjusted to the surface applying a very simple single column approach. Over the ocean an adjustment factor is applied, which is a function of radius from the center ranging from 0.9 to 0.7, and the winds are turned 20 degrees toward low pressure. Over land, the oceanic winds are reduced by an additional 20% and turned an additional 20 degrees toward low pressure.

Gotta wonder how reliable this methodology is for a system that doesn't have a well-defined surface circulation yet.

[srainhoutx]

I might give it a 40-50% shot at developing by Wed/Thu.

Interesting. Thanks for the update wxman57.

[x-y-no]

Note that as stated above, they make assumptions that a mid-level (700mb/10,000ft) circulation extends down to the surface. That's not necessarily the case here. Surface obs in the area do not indicate any LLC.

What concerns me is that we do have a moderate to strong wave moving westward beneath a predicted building upper high vs. into 40 kts of shear like 92L. I might give it a 40-50% shot at developing by Wed/Thu.

Looks like we were typing simultaneously.

I share your concern about this system in the 2 to 3 day and onward timeframe. I was just a bit skeptical of this particular product giving reliable data in the context of an invest (as opposed to a developed cyclone.)

[KWT]

If I were the forecasters I wouldn't decrease the chances just because convection died out during the day which is to be expected. If the overall trend were that the convection was dieing then yes. but They just increased the chances this morning which is hardly enough time to see a overall pattern suggestive of a invest dieing. If they based it on the convection from update to update then every morning they would increase the chances and every evening they would decrease the chances which wouldn't look very good for them. The general over view for 93L is that it's a active tropical wave moving into an area of lighter wind shear, over boiling hot water with plenty of oceanic heat content to power a cat 4 or 5 sub-900mb Hurricane.

Quite often they did actually drop it and raise it based on some longer lasting convective bursts/weakening phases, not by much but usually they were prepared to drop it or raise it 10% based on 6-12hr trends in convection.

As wxman57 said its got a shot, esp a little further down the line when it moves into the W.Caribbean with an upper high present over the system in that region.

[HURAKAN]

360
ABNT20 KNHC 212349
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT MON JUN 21 2010

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

#5
A VIGOROUS TROPICAL WAVE LOCATED FROM EASTERN HISPANIOLA SOUTHWARD
OVER THE CENTRAL CARIBBEAN SEA IS PRODUCING WIDESPREAD CLOUDINESS
AND SHOWERS ACROSS MUCH OF THE CENTRAL AND EASTERN CARIBBEAN SEA...
HISPANIOLA...PUERTO RICO...AND NORTHERN VENEZUELA. THIS DISTURBANCE
CONTINUES TO SHOW SIGNS OF INCREASED ORGANIZATION...AND UPPER-LEVEL
WINDS ARE CONDUCIVE FOR A TROPICAL DEPRESSION TO FORM DURING THE
NEXT COUPLE OF DAYS. THIS WEATHER SYSTEM COULD PRODUCE LOCALLY
HEAVY RAINFALL AND GUSTY WINDS OVER PORTIONS OF PUERTO RICO...THE
DOMINICAN REPUBLIC...HAITI...AND THE NETHERLANDS ANTILLES DURING THE
NEXT DAY OR SO AS THE SYSTEM MOVES WEST-NORTHWESTWARD AT 10 TO 15
MPH. THERE IS A MEDIUM CHANCE...50 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER STEWART

[cycloneye]

That is a very strong language in a TWO that assure things look good for development.

[Ivanhater]

I think they saw Wxmans post

Seriously though, a long week shaping up it seems

[KWT]

Yeah the structure has improved with this system, but convection is still rather on the tame-side, I think though as it pulls away from SA and moves under the building upper high conditions aloft look decent enough for development.

I think thats why the TWO is bullish...

[Aric Dunn]

:uarrow: That is a very strong language in a TWO that assure things look good for development.

not only that its from stewart !! very very reliable

[Aquawind]

50% with no defined LLC must mean they are expecting the condusive conditions ahead to make it happen.

[KatDaddy]

Yep and the GOM is very warm. This will be the big ticket item for the media.......TS Alex and the BP oil spill. I am scheduled to fly out to
Salt Lake City next Monday and return next Friday. I hope this stay away from the Upper TX Coast. It way to early to say where this will
end up and how strong it will be.

[SunnyThoughts]

Big ticket item for the media indeed. Wall to wall blitz coming by Thursday or Friday probably, IF this does indeed strengthen and head to the gulf. Thanks to everyone for their insights and the satellite pics.

[KWT]

50% with no defined LLC must mean they are expecting the condusive conditions ahead to make it happen.

Indeed, not all that surprising though given you've got quite a decent upper high forecasted to develop right over the disturbance, so conditions really are going to be pretty decent, esp over W.Caribbean and when its away from SA.

[Frank2]

What the system seems to lack is good vorticity. Perhaps this is what the models are forecasting - no rotation to spark a cyclone.

Jeff Masters also mentioned that in his blog...

Certainly it's not lacking for moisture, that's for sure...

Have a good evening everyone,

Frank

[Ivanhater]

AXNT20 KNHC 212357
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT MON JUN 21 2010

...SPECIAL FEATURES...

THE WAVE IS ACCOMPANIED BY A LARGE AREA OF DEEP LAYER
MOISTURE THAT COVERS THE ENTIRE ERN HALF OF THE CARIBBEAN
EVIDENT IN TOTAL PRECIPITABLE WATER IMAGERY. BROAD LOW TO
MID-LEVEL CYCLONIC FLOW IS ABOUT THE WAVE. IT APPEARS THAT A
SURFACE CIRCULATION IS TRYING TO FORM W OF THE WAVE AXIS NEAR
14N72W SEEN IN THE LAST VISIBLE SATELLITE IMAGERY OF THE DAY.

[clfenwi]

What the system seems to lack is good vorticity. Perhaps this is what the models are forecasting - no rotation to spark a cyclone.

Jeff Masters also mentioned that in his blog...

Certainly it's not lacking for moisture, that's for sure...

Have a good evening everyone,

Frank

Looking at the UW-CIMSS TPW graphic, there seems to be some cyclonic rotation in the area of interest starting in the past few hours. Hmm.

[HURAKAN]

00z

AL, 93, 2010062200, , BEST, 0, 149N, 700W, 25, 1010, WV

wave reaches 70°W

[Aquawind]

I missed this mornings ASCAT.. It does show some interesting barbs on the western edge.