ATL: INVEST 91L - Discussion

[HURAKAN]

yeah, shear induced. Foreast to let up any?

[Ivanhater]

Well nearly every model does develop this system once in he gulf..all be it sheared, but a tropical system non the less..I think development chances are more likely than not...

[HURAKAN]

Heavy rains from 91L kill 11 in Honduras

Posted by: JeffMasters, 9:37 AM EDT on October 21, 2008

A week of heavy rains over northern Honduras, northern Guatemala, and Belize due to Tropical Depression Sixteen and a Western Caribbean tropical disturbance (91L) have resulted in record flooding and deadly mudslides across the region. In Honduras, a nationwide state of emergency has been declared, and at least eleven people are dead and two missing from the flooding. Two large landslides blocked the Coyol River in western Honduras yesterday, forming a lake 500 feet deep. Engineers are attempting to drain the lake today, but they won't be helped by the weather--91L promises to move little the next two days, and will continue to dump heavy rains on the region. In Belize, damage is already estimated in the ten of millions, and some areas are seeing flooding worse than was experienced during Hurricanes Mitch and Keith. Satellite estimates (Figure 1) suggest up to a foot of rain has fallen over the region in the past week.

Visible satellite loops show that the intensity and areal coverage of 91L's heavy thunderstorms have remained about the same the past 12 hours, and are primarily affecting Belize and the east coast of Mexico's Yucatan Peninsula this morning. The storm is located too close to land to develop into a tropical depression, and wind shear is also rather high, 20 knots.

The forecast for 91L
Wind shear is expected to remain in the 15-25 knot range over the next three days. Steering currents are weak, and little movement is likely through Wednesday. Heavy rains will affect northern Honduras, northern Guatemala, Belize, Mexico's eastern Yucatan Peninsula, western Cuba, and the Cayman Islands through Wednesday. A trough of low pressure swinging across the Midwest U.S. should be able to start pulling 91L northward or northwestward by Thursday. Once 91L enters the Gulf of Mexico on Thursday, the trough should swing the storm to the northeast, bringing it across the west coast of Florida between Tampa and the Big Bend region on Friday night. Wind shear will be very high over the Gulf of Mexico this week, in the 30-40 knot range, and 91L is expected to make a transition to a very wet extratropical storm by Friday. The storm should bring sustained winds of 30-35 mph and heavy rains of 2-3 inches to Florida.

[HURAKAN]

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT TUE OCT 21 2008

CARIBBEAN SEA...
A 1011 MB SURFACE LOW IS OVER THE GULF OF HONDURAS NEAR 16N88W.
BROAD LOW LEVEL CONVERGENCE AROUND THIS LOW...COMBINED WITH
UPPER LEVEL DIVERGENCE TO THE SE OF AN UPPER LEVEL WIND SPEED
MAXIMUM IN MOIST SOUTHWESTERLY FLOW ALOFT...IS SUPPORTING
SCATTERED MODERATE/ISOLATED STRONG CONVECTION PARTICULARLY NE OF
THE SURFACE LOW FROM 16N-20N BETWEEN 83W-89W. THIS INCLUDES
PORTIONS OF THE NW CARIBBEAN SEA AND ADJACENT INLAND AREAS OF SE
MEXICO AND CENTRAL AMERICA. SIGNIFICANT DEVELOPMENT OF THIS
SYSTEM IS NOT EXPECTED DUE TO ITS PROXIMITY TO LAND.
HOWEVER...LOCALLY HEAVY RAINS ARE POSSIBLE OVER PORTIONS OF
HONDURAS...GUATEMALA...BELIZE...AND THE YUCATAN PENINSULA DURING
THE NEXT COUPLE OF DAYS. FARTHER TO THE NE...A WEAKENING
STATIONARY FRONT EXTENDS FROM E CUBA NEAR 21N77W TO 21N82W TO
THE N YUCATAN PENINSULA NEAR 20N87W. ATMOSPHERIC LIFT IN MOIST
SOUTHWESTERLY FLOW ALOFT NEAR THIS FRONT IS SUPPORTING SCATTERED
MODERATE CONVECTION WITHIN 60 NM EITHER SIDE OF THE FRONT
BETWEEN 76W-82W...AND COULD BE ENHANCING THE CONVECTION
ASSOCIATED WITH THE AFOREMENTIONED SURFACE LOW.

[HURAKAN]

WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
0830 AM EDT TUE 21 OCTOBER 2008
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 22/1100Z TO 23/1100Z OCTOBER 2008
TCPOD NUMBER.....08-143

I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY.....NEGATIVE.

II. PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK.....NEGATIVE.
JWP

[Blown Away]

SHIP S 1200 17.40 -86.40 33 316 300 9.9 - 1.6 1.0 - - 29.77

29.77 inHg = 1008.1 mb

Is that a relocation of the low center?

Is the new low center now at 17.40N/86.40W?

[HURAKAN]

SHIP S 1200 17.40 -86.40 33 316 300 9.9 - 1.6 1.0 - - 29.77

29.77 inHg = 1008.1 mb

Is that a relocation of the low center?

Is the new low center now at 17.40N/86.40W?

It's possible that a new center is trying to develop. 300 is not west but very close. There is always the question of how accurate a ship measurement is.

[Ed Mahmoud]

Looking at satellite loops, screaming shear just to the North, and Havana had dewpoints just pushing above 70ºF now.





In my extremely unprofessional and not to be trusted unofficial opinion , this has little future as a purely tropical cyclone.



All is not lost, however, for fans of sub-tropical action. Although it shear is near 50 knots just to its North, it has plenty of moisture with it, and a super-mondo upper low is diving into the nations mid-section, and if one accepts the 0Z GFS solution, which I think is in the ballpark, if not exactly correct, a juiced up extra-tropical or perhaps sub-tropical storm may develop in the Gulf, perhaps fairly far North, and head into Florida.



Might even be a tornado threat for the Eastern Gulf coast. 0Z GFS soundings, for example, show over 600 m^2/s^2 helicity, although low level instability is extremely limited.

[Sanibel]

Pulling up NW now and probably a curve into N.

Been sitting too long in one place.

From satellite at low-level some kind of forcing is happening now increasing development.

[Blown Away]

Are the getting ready to deactivate 91L, no model runs since 00z??

[HURAKAN]

[boca]

I think 91L will be deactivated especially that its not getting better organized.I haven't seen any recent runs either.

[Dean4Storms]

Does look like it is moving NNW now.

[gatorcane]

I think 91L will be deactivated especially that its not getting better organized.I haven't seen any recent runs either.

That would not make sense. It's sheared but its the best it has looked relatively speaking. It looks to me a subtropical or tropical low is in the making as I have been predicting.

As for the shear, there will be a period of time the shear will lighten some as it moves NNW...just before the next trough approaches but then shear does pick up again.

You can see the area of negative shear tendency in the WGOM that will move east as the ridge moves east into the Atlantic.

[wxman57]

gatorcane,

I think you must be looking at a different disturbance than I am. I see an inverted trof now - no more circulation. Pressures are rising all across the NW Caribbean, up to 1017.4 MB in the area now. Wind shear remains high and is only going to increase as the moisture is drawn northward. Chances of tropical development appear to be decreasing.

Here's a current analysis. I can see some slight turning near 17.8N/87.2W just approaching the Yucatan. There's a large outflow boundary moving from east to west across the inverted trof axis now. Pressures, like I said, are relatively high (as is shear):

[Tampa Bay Hurricane]

****EDITED after reviewing pro-met analysis****

***Not Official***

A lot more convection, I think the center may relocate
further offshore,

But there is tons of shear so I think a baroclinic extratropical maybe
subtropical storm but most likely baroclinic will bring 50 mph winds to much of florida
in thunderstorms.

[Ivanhater]

Wxman, let me have some end of season disagreement with you before class

Just taking a look at the models, they dont develop this until it exits the yucatan then gets in the gulf...cmc, gfs, nogaps, ukmet, gfdl all have at least a subtropical storm hitting the panhandle bigbend area. Though it does seem like it will be sheared and not strong..but good model agreement non the less...

[AJC3]

Wxman, let me have some end of season disagreement with you before class

Just taking a look at the models, they dont develop this until it exits the yucatan then gets in the gulf...cmc, gfs, nogaps, ukmet, gfdl all have at least a subtropical storm hitting the panhandle bigbend area. Though it does seem like it will be sheared and not strong..but good model agreement non the less...

The development over the GOMEX is baroclinic. Look at the position of the H25 jet, the H50 trough, the broad extent of upward VV and SLP falls. Low pressure is not developing in the face of strong shear...it's developing because of the dynamic forcing that's also causing the shear.

[Blown Away]

Anybody seeing a possible LLC near 17N/86.4W moving NW? Or is it an eddy?
http://www.ssd.noaa.gov/goes/flt/t1/loop-vis.html

[Tampa Bay Hurricane]

Wxman, let me have some end of season disagreement with you before class

Just taking a look at the models, they dont develop this until it exits the yucatan then gets in the gulf...cmc, gfs, nogaps, ukmet, gfdl all have at least a subtropical storm hitting the panhandle bigbend area. Though it does seem like it will be sheared and not strong..but good model agreement non the less...

The development over the GOMEX is baroclinic. Look at the position of the H25 jet, the H50 trough, the broad extent of upward VV and SLP falls. Low pressure is not developing in the face of strong shear...it's developing because of the dynamic forcing that's also causing the shear.

AJC3 and Wxman57, a question:

Will I still get to feel some 40-50 mph gusts at the beach along the west coast
tampa bay? Cause extratropical systems can have big windfields? That would be AWESOME
to be at the beach in.

I'm a storm-chasing wild surfing nut