Lesser Antilles Disturbance 97L a Threat to Develop

By: Dr. Jeff Masters , 2:46 PM GMT on September 01, 2013

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A tropical wave over the Lesser Antilles Islands (Invest 97L) is moving westward at 15 mph, and is bringing heavy rains and gusty winds to the islands. Top sustained winds in the islands as of 10 am AST Sunday were 26 mph at Monserrat. Heavy thunderstorm activity has sharply increased since Saturday, as seen on satellite loops. A large circulation is evident, with some westerly winds blowing to the south of the disturbance. However, the thunderstorms are poorly organized, and there is no sign of a well-organized surface circulation. Martinique radar shows some rotation to the echoes, though well-organized spiral bands are not evident, and do not appear to be forming. Wind shear has dropped to a moderate 10 - 20 knots over the system. An area of dry air from the Saharan Air Layer (SAL) surrounds 97L and is interfering with development.


Figure 1. Latest satellite image of Invest 97L.

Forecast for 97L
Wind shear is expected to be in the low to moderate range for the next five days, and ocean temperatures will be warm, 28 - 29°C. The disturbance is steadily moistening the atmosphere and is moving into a moister environment, so dry air will be less of an impediment to development as the week progresses. The main factor keeping the disturbance from developing over the next two days would appear to be the fact that 97L is quite large, and is stretched out from east to west over a wide expanse. Large, elongated systems like 97L usually take several days to consolidate and spin up. Another factor that will likely retard development is the presence of strong surface trade winds over the Eastern Caribbean ahead of 97L, south of the Dominican Republic. These strong trade winds are a common feature of the Eastern Caribbean, and make the region something of a hurricane graveyard. As the surface wind flow to the west of 97L accelerates into this wind max, air will be sucked from aloft downward towards the surface, creating sinking air, interfering with the formation of thunderstorm updrafts. The best chance for development of 97L would appear to be on Wednesday or Thursday, when the disturbance reaches the Central Caribbean. The wave will likely spread heavy rains to Puerto Rico, the Virgin Islands, and the Dominican Republic by Tuesday, and to Haiti by Wednesday. These rains will be capable of causing life-threatening flash flooding and mudslides in mountainous regions in Puerto Rico and Hispaniola. Of our three reliable models for predicting genesis, the UKMET, GFS, and European models, only the UKMET model develops the disturbance, predicting it will become a tropical depression south of Haiti on Wednesday, and near Jamaica on Thursday. In their 8 am EDT Sunday Tropical Weather Outlook, NHC boosted the 5-day odds of formation of 97L to 30%, and the 2-day odds to 20%.


Video 1. You can see why landslides triggered by heavy rains from a tropical cyclone are among the most dangerous hazards of these storms, thanks to a dashboard cam that caught this extraordinary rock slide in Northeast Taiwan on August 31, 2013, after heavy rains from a cold front drenched the island with up to 200 mm (7.87") of rain in 24 hours. The rains fell upon soils already saturated by Thursday's torrential rains from Tropical Storm Kong-Rey, which dumped up to 482 mm (19") of rain on Taiwan, killing three people. The driver of the car caught in the rock slide survived with minor injuries. Thanks go to wunderground member Robert Speta for bringing this video to my attention. A separate video showing the damage to the car and the course of the rock slide is here.

Jeff Masters

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I still think the storm will lie on the south side of the guidance ...however there could be a tough capable of pulling the storm out of the Caribbean sea and out to sea....a little to early to say though
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Quoting 647. PanhandleChuck:
Finally, something to nibble on and hush the G.W. rhetoric!

Looking forward to all of the predictions from Mexico to NYC. LOL


Funny, you are the first to mention anything about GW. Wonder why that is . . .
Member Since: June 25, 2011 Posts: 2 Comments: 3731
Quoting 651. MiamiHurricanes09:
Completely anticipated. With surface convergence this unimpressive, it's bound to struggle tonight convectively.



Best guess it'll be gone nearly completely by 00z.
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652. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 5698
Quoting 645. GatorWX:
See you all in a few hours. We'll see what happens. Until then, looks like dmin is approaching.

Completely anticipated. With surface convergence this unimpressive, it's bound to struggle tonight convectively.

Member Since: September 2, 2009 Posts: 130 Comments: 21109
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Quoting 639. whitewabit:


Navy has it at 14.6N-59.7W

Yeah. I'm going off of Satellite low level inflow. Which is hinting at the circulation hanging back more toward the Convection.
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Quoting 644. MiamiHurricanes09:
My bad, should work now.


It's all good, I can see it now.

Well, that doesn't look good!
Member Since: October 8, 2008 Posts: 14 Comments: 4553
Finally, something to nibble on and hush the G.W. rhetoric!

Looking forward to all of the predictions from Mexico to NYC. LOL
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Quoting Stormchaser2007:


Yeah, I should have clarified.


I'm still sticking with the BAMS and BAMM until we get a COC everyone agrees on and the models can stop using bogus vortexes.
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See you all in a few hours. We'll see what happens. Until then, looks like dmin is approaching.

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Quoting 641. caneswatch:


I can't see it.
My bad, should work now.
Member Since: September 2, 2009 Posts: 130 Comments: 21109
From last evening 00Z


SYNOPSIS 2013090100

P25L … 97L
15N, 55W
850 hPa

Because 97L is a bit weaker and closer to the islands and a potential upper-level low there, it is becoming more difficult to track at 700 hPa, at least in ECMWF and GFS. So I drop down to 850 hPa today.


ECMWF: I track the pouch as it moves westward across the eastern Caribbean, keeping P25L/97L weak and not developing. However, during the last couple days, ECMWF breaks off the northeastern portion (and combines with a following wave) and develops it as a separate pouch ending up northeast of Hispaniola at 120 hours.

GFS: Similar to ECMWF concerning a weak, non-developing P25L/97L being tracked across the Caribbean. GFS also breaks off a northeastern portion that tracks along the northern coast of Puerto Rico and Hispaniola, but it does not intensify. Instead, GFS develops the following wave ("New Hope") into a small but relatively intense circulation that ends up farther to the northeast ~22N, 63W at 120 hours.

UKMET: Continues to develop P25L/97L, ending up near at the southeastern tip of Haiti at 120 hours. Because 97L itself strengthens, UKMET does not break off a northeastern portion. However, consistent with previous forecasts, UKMET develops the following wave quite strongly, but it ends up much farther south (15N,62W) than in GFS.

NAVGEM:

HWRF-GEN:



ECMWF -4.7 v850 120h
GFS -6.2 v700 120h
UKMET -4.2 v700 120h
NAVGEM ---- ---- ---h
HWGEN ---- ---- ---h





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Quoting 636. SuperStorm093:
Hispaniola might disrupt the storm big time if it moves there.



It would. The new output shows it having a lot of land interaction
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Quoting 640. MiamiHurricanes09:
12z HWRF.



I can't see it.
Member Since: October 8, 2008 Posts: 14 Comments: 4553
12z HWRF.

Member Since: September 2, 2009 Posts: 130 Comments: 21109
639. whitewabit (Mod)
Quoting 627. TylerStanfield:

The Circulation is relocating closer to 59W and is trying to stack with the Midlevel center, and the leftover vortmax to 97L's west is slowly dissipating. Given the current trends and if they were to continue (Keep in mind DMIN is already approaching and should hinder the system some), I would expect a Tropical Depression to form later in the day Monday.


Navy has it at 14.6N-59.7W
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Quoting 635. 954FtLCane:
The more I look at the future track of 97 the more I see the eastern Gulf, all of FL and the Bahamas in it's path.
As mentioned before it is way too early to point a current non-storm in any direction but if I were a gambling man and had to choose right now I would pick Florida because it's sticking out there like a sore thumb.
yes im with you..florida needs to keep a good eye in this storm..remember we are in sept now and...........
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Hispaniola might disrupt the storm big time if it moves there.
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The more I look at the future track of 97 the more I see the eastern Gulf, all of FL and the Bahamas in it's path.
As mentioned before it is way too early to point a current non-storm in any direction but if I were a gambling man and had to choose right now I would pick Florida because the models seem to be pointing that was and it's sticking out there like a sore thumb.
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Quoting CybrTeddy:


edit -- just saw the 18z output.


Yeah, I should have clarified.

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Quoting 625. CybrTeddy:


Doesn't look likely it will, if one were to believe the statistical models. Could be something if it pulls together before reaching the central Caribbean.


If it develops in Eastern Caribbean it may turn more NW.
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Hot off the presses...

TAFB keeps 97L well to the south of the GA

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Quoting 591. MississippiWx:


Due to the current convective structure and the overall large circulation, it wouldn't surprise me to see the center hang back a bit or even develop further to the east a bit.


Yes, although its suppose to be moving at 15kts it has been moving a lot slower than that since 8pm due to center reformations. Once that convection on the eastern of the center slip over it around 60W or 61W then cyclogenesis should occur.
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This is from 12z GFS. Must be low #2 shown on NAVGEM and CMS 12Z.
Member Since: August 2, 2011 Posts: 0 Comments: 1871
Inflow on the southern side seems to be improving very nicely.

Member Since: September 2, 2009 Posts: 130 Comments: 21109
Quoting 610. Hurricanes305:
97L continues to organize and improves its structure. In the last couple frame of vis sat you can see the beginning of some low level convective banding forming this indicates the equatorial inflow is moist. Outflow is becoming more defined to the north as well. It still need the shed its extra vort especially to its SW which will take the rest of the day to do but once complete it should stacked up quickly and develop by the overnight hours into the early morning if current trends continues.



I agree with the NHC stances as they are taking this much more seriously as a threat down the road.

The Circulation is relocating closer to 59W and is trying to stack with the Midlevel center, and the leftover vortmax to 97L's west is slowly dissipating. Given the current trends and if they were to continue (Keep in mind DMIN is already approaching and should hinder the system some), I would expect a Tropical Depression to form later in the day Monday.
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This ain't good ladies and gentlemen
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Quoting 614. Stormchaser2007:
Obviously, it would be in 97L's best interest to not move near or into Hispaniola



edit -- just saw the 18z output.
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Quoting 620. KEEPEROFTHEGATE:

Tropical Cyclone Formation Alert (TCFA) 97L
‎Today, ‎September ‎1, ‎2013, ‏‎40 minutes ago | CDO.FWC.NRFK.fct@navy.mil (FWC-N CDO)Go to full article
Issued: Sun 01 Sep 2013 15:00Z
Tropical Cyclone Formation Alert Graphic
Tropical Cyclone Formation Alert Text
Tropical Cyclone Formation Alert JMV data
Tropical Cyclone Formation Alert Gold Ovly
FNMOC Satellite Data Tropical Cyclone Page

Fasten your seatbelts! It's gonna be a wild ride!
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622. JRRP
Quoting Stormchaser2007:
Obviously, it would be in 97L's best interest to not move near or into Hispaniola


yeah
Member Since: August 16, 2007 Posts: 0 Comments: 5698
Quoting 614. Stormchaser2007:
Obviously, it would be in 97L's best interest to not move near or into Hispaniola




that would be vary bad news if it did
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Tropical Cyclone Formation Alert (TCFA) 97L
‎Today, ‎September ‎1, ‎2013, ‏‎40 minutes ago | CDO.FWC.NRFK.fct@navy.mil (FWC-N CDO)Go to full article
Issued: Sun 01 Sep 2013 15:00Z
Tropical Cyclone Formation Alert Graphic
Tropical Cyclone Formation Alert Text
Tropical Cyclone Formation Alert JMV data
Tropical Cyclone Formation Alert Gold Ovly
FNMOC Satellite Data Tropical Cyclone Page
Member Since: July 15, 2006 Posts: 170 Comments: 53526
Quoting 605. sar2401:

I'm not a good enough fortune teller to make that kind of judgement. Give it five days and we'll see.

A trough will be in place over the east and the faster it develops the sooner it will trun north probably in the vicinity of Hispanola.
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Quoting 615. KEEPEROFTHEGATE:
training mission now going to switch to recon mission later 24 hrs or so

Thank you!
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Saw this backwards low on the meteorological images of july and august 2013 on the home page.

Found it interesting because I was at NCEP when in their official wx briefing, they were debating which model was right about how this low would progress, and they decided that this solution most likely.


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.
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Quoting 607. 62901IL:

Uhm...what are they doing? There isn't an AOI to watch off the coast of Florida.
training mission now going to switch to recon mission later 24 hrs or so
Member Since: July 15, 2006 Posts: 170 Comments: 53526
Obviously, it would be in 97L's best interest to not move near or into Hispaniola

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Quoting 607. 62901IL:

Uhm...what are they doing? There isn't an AOI to watch off the coast of Florida.


Er, that's the NOAA G 4 "Gonzo" dropping air sampling sondes around the system.

Up round 38,000 ft.





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Quoting 610. Hurricanes305:
97L continues to organize and improves its structure. In the last couple frame of vis sat you can see the beginning of some low level convective banding forming this indicates the equatorial inflow is moist. Outflow is becoming more defined to the north as well. It still need the shed its extra vort especially to its SW which will take the rest of the day to do but once complete it should stacked up quickly and develop by the overnight hours into the early morning if current trends continues.



I agree with the NHC stances as they are taking this much more seriously as a threat down the road.



I think we could see a upgrade at 11pm tonight
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wayyyyyyyyyyyyyyyyyy too early to give a destination for 97L
Member Since: September 19, 2005 Posts: 2 Comments: 4131
97L continues to organize and improves its structure. In the last couple frame of vis sat you can see the beginning of some low level convective banding forming this indicates the equatorial inflow is moist. Outflow is becoming more defined to the north as well. It still need the shed its extra vort especially to its SW which will take the rest of the day to do but once complete it should stacked up quickly and develop by the overnight hours into the early morning if current trends continues.



I agree with the NHC stances as they are taking this much more seriously as a threat down the road.
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Quoting 603. 62901IL:
Oh dear. It appears that most of us are thinking a major hurricane for the gulf coast. I certainly hope that doesn't happen!
i was looking at a weather map for this week, seems 2-3 highs will be sitting up on the northern gulf coast..that could be a blocker if it verifies..not too good for central florida tho if it does go into the gulf.
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NOLA Disco

No Big Front late in the period,

Long term...
eastern side of the upper ridge will continue to erode Monday as
upper level trough over the Great Lakes amplifies and digs deeper
across the eastern half of the country. At the same time...surface
high over the central Gulf will shift eastward enough for onshore
flow to bring back middle level moisture to the area. Model soundings
support this with precipitation water values increasing from 1.6 yesterday
to over 2 inches by Monday. The combination less subsidence from
lowering heights and more moisture in the column will be increased
shower and thunderstorm activity. Have maintained previous forecast
of 40 percent chance of showers and thunderstorms for Monday.


Rain chances will stay increased through midweek as weak frontal
boundary associated with the trough finally makes its way to the
County Warning Area. The front will likely stall and dissipate but not before
becoming the focus for higher rain chances.
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Quoting 602. Patrap:
Product: NOAA High Density (HDOB) Message (URNT15 KWBC)
Transmitted: 1st day of the month at 18:08Z
Date: September 1, 2013

Aircraft: Gulfstream IV-SP (G-IV) (Reg. Num. N49RF)

Mission: Training Mission (flight in the North Atlantic basin)

Observation Number: 15

18:08:30Z 27.717N 82.483W 848.1 mb
(~ 25.04 inHg) 1,576 meters
(~ 5,171 feet) 1016.1 mb
(~ 30.01 inHg) - From 218° at 3 knots
(From the SW at ~ 3.4 mph) 18.9°C
(~ 66.0°F) -2.5°C
(~ 27.5°F) 4 knots
(~ 4.6 mph) - - - -
Time Coordinates Aircraft
Static Air Pressure Aircraft
Geopotential Height Extrapolated
Surface Pressure D-value Flight Level Wind (30 sec. Avg.) Air Temp. Dew Point Peak (10 sec. Avg.)
Flight Level Wind SFMR
Peak (10s Avg.) Sfc. Wind SFMR
Rain Rate Estimated Surface Wind (30 sec. Avg.)
Using Estimated Reduction Factor Peak Wind at Flight Level to
Est. Surface Reduction Factor

HDOB Observations

Independent Calculations from Tropical Atlantic

At 17:59:00Z (first observation), the observation was 50 miles (80 km) to the N (5°) from Fort Myers, FL, USA.

Uhm...what are they doing? There isn't an AOI to watch off the coast of Florida.
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ouch

Prob of RI for 25 kt RI threshold= 33% is 2.8 times the sample mean(11.9%)
Prob of RI for 30 kt RI threshold= 15% is 2.0 times the sample mean( 7.6%)
Prob of RI for 35 kt RI threshold= 7% is 1.6 times the sample mean( 4.6%)
Prob of RI for 40 kt RI threshold= 6% is 2.0 times the sample mean( 3.0%)
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Quoting interpreter:

Looking good but NO threat to the US.

I'm not a good enough fortune teller to make that kind of judgement. Give it five days and we'll see.
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.