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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Popcorn convection showing up all around the invest, and no outflow boundaries yet. Still way too early to say if it's weakening. The aforementioned popcorn convection can signal a forthcoming larger burst.
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Quoting GatorWX:
96L, still there, but don't look good.

Nice rotation, nevertheless...
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Quoting 390. CybrTeddy:


And here we go, the mood will go from "we'll have to watch this for significant development" to "season is a bust," by 5pm.


Why do we have to wait until 5pm!?! Why can't we claim it's a bust now!?
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Peronally, I would give Invest 97L a 30% chance of development within 48 hours but a 60% chance of development within 120 hours. There aren't too many limiting factors besides the East Caribbean and its broad circulation size.
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Member Since: August 2, 2010 Posts: 0 Comments: 2000
Boy...97L seems to have escalated in the last 12 hours...I did a special post on my blog real quick because of that....

As far as the eastern Caribbean trade winds dampening things down...yes it can happen but this isn't always the case. For instance as we entered the month of September in 2007...Felix spun up while moving into the eastern Caribbean.
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Quoting 396. Gearsts:
I'm not the one saying this will turn in to a hurricane.


Nah, I'm not talking about you - the blog's optimistic mood will be replaced by one with shear agony and pessimism by 7pm.
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Quoting 390. CybrTeddy:


And here we go, the mood will go from "we'll have to watch this for significant development" to "season is a bust," by 5pm.
I'm not the one saying this will turn in to a hurricane.
Member Since: August 2, 2010 Posts: 0 Comments: 2000
395. SLU
Barbados. TBPB

1:00 PM 84.2 °F 94.1 °F 77.0 °F 79% 29.83 in 6.2 mi West 23.0 mph - N/A Rain Light Rain Showers
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Interesting last frame of the CMC in addition to 97L wants to develop a secondary low that will pull northeastward out of the Caribbean. Don't know whether to buy into that solution or if this is more a case of convective feedback?

Member Since: June 30, 2013 Posts: 12 Comments: 8774
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Someone needs to sit down and drink a cup of haterade.I'm sure you can bring something more than hate to a weather blog can't you?
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Think the low back at 48W is shown by some models to make it to the Bahamas


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Quoting 352. Gearsts:
Convection warming


And here we go, the mood will go from "we'll have to watch this for significant development" to "season is a bust," by 5pm.
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Quoting 161. CosmicEvents:
This is like saying 97L is an elephant, and all it's really missing is a trunk.
.
One or 2 of you seem to maybe be a bit ahead of the situation.
Only one or 2... lol

Quoting 181. Tropicsweatherpr:


We need QuickScat badly.
I'm wondering how on schedule we are for the replacement satellite, given the financial perambulations of the last few years...

Wasn't the replacement due for launch in 2014? or was it 2018?

Quoting 185. GwadaGeek:
Good Morning everybody.
Here in Guadeloupe, little wind & little rain for the moment.
Here is the link to a webcam in St François Guadeloupe. View of the laggoon. http://www.plage-guadeloupe.fr/index.php/la-webca m
Merci beaucoup.

Quoting 191. Tazmanian:



there you are I new you come out of hiding some day
This is the once per day dose of the blog... bitter, yet invigorating, like bush medicine...

lol


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Notice, as I mentioned earlier, now the updated sfc maps show a continued westerly, not northwesterly, movement.


Member Since: July 9, 2006 Posts: 184 Comments: 29610
Quoting 384. GatorWX:
96L, still there, but don't look good.



..but not horrible. Not much shear and an anticyclone sitting over it. Doubt the little ball of convection persists. Looks to be struggling quite a bit.
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(Tampa bay area)...August was a wet month across much of the area. Only a few areas had below-average rainfall. Here's a sampling of totals from the region:
Bradenton, 10.37
Ellenton, 9.90
Floral City, 3.65
Inverness, 3.08
Lakeland, 8.54
Land O' Lakes, 4.88
Planty City, 8.23
Ruskin, 7.64
Safety Harbor, 16.77
St. Leo, 1.35
St. Petersburg, 6.89
Tampa, 11.91 inches
Tarpon Springs, 15.19
Westchase, 12.52
Winter Haven, 6.31
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96L, still there, but don't look good.

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Quoting 378. JRRP:
Facepalm!
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Quoting 378. JRRP:
According to this MJO is still in the east pacific, correct?
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THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL FLORIDA.

.DAY ONE...TODAY AND TONIGHT.

.THUNDERSTORM IMPACT...
CONTINUING SOUTHWEST FLOW WILL ONCE AGAIN DELAY THE ONSET OF THE
EAST COAST SEA BREEZE UNTIL THE EARLY TO MID AFTERNOON ESPECIALLY
ALONG THE VOLUSIA COAST. THE MAIN FOCUS FOR STORMS TODAY WILL BE
WITH THE DOMINANT WEST COAST SEA BREEZE THAT WILL PUSH INTO THE
INTERIOR DURING THE EARLY TO MID AFTERNOON. A FEW LIGHTNING STORMS
MAY DEVELOP ALONG THE TREASURE COAST AROUND MID DAY AS THE EAST
COAST SEA BREEZE INTERACTS WITH THE LAKE OKEECHOBEE BREEZE.

COVERAGE OF LIGHTNING STORMS WILL INCREASE LATE THIS AFTERNOON
INTO THIS EVENING AS THE SEA BREEZES COLLIDE OVER THE EASTERN HALF
PENINSULA LATE IN THE DAY. WITH THE BEST COVERAGE AFTER 4 PM
STRETCHING FROM VOLUSIA COUNTY SOUTHWARD TO OSCEOLA COUNTY.

A FEW OF THESE STORMS SHOULD CONTAIN FREQUENT LIGHTNING
STRIKES...GUSTY DOWNBURST WINDS UP TO 50 MPH...SMALL HAIL...AND
LOCALLY HEAVY RAIN. STORM MOTION WILL BE TOWARD THE NORTH-
NORTHEAST AROUND 15 MPH WHICH WILL BRING A FEW STORMS TO THE COAST
THIS EVENING.
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Yes, I know this isn't current per se:

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With all the rhetoric about 97L, we are due for things to just pop up.
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378. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 6213
From my Weather Information Systems class:

"Deterministic models (RUC, NAM, GFS) have highest grid resolution, most complete physics packages, but do not provide any information on forecast uncertainty.

Ensemble models (SREF, etc.) have lower resolution, but provide users with uncertainty of forecast as well as determining the most probable forecast state."


Member Since: June 30, 2013 Posts: 12 Comments: 8774
Quoting 367. java162:
my bet is the coc is around 15n 58w..... this is where the thunderstorms seem to be the most intense and persistent


That is probably the MLC.
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Quoting 340. GatorWX:

Click for animation and speed it up fast as it'll go. Pretty indicative of a very stretched low.



I'd keep an eye on that east side. Bet the western portion of convection collapses over the next couple hours, much as it did earlier. There's still an evident circulation out west associated with that collapsed convection.


With that said, the circulation out west is the one we were following early this morning. It has since died out convection-wise. I'm going to assume the same is happening in the central vorticy. The one furthest east is at the ne periphery of the 850mb vorticy, leading me to believe the energy associated with this feature is progressing in that direction. I'd watch it if anything is to happen today. If it simply keeps spinning up vorticies, it may take a lot longer than it appears presently. My three cents, cause as I've stated before, two just ain't enough. :)
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Quoting 350. sunlinepr:
One path is over Hispanola, other interacts with SA.
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373. beell
From a Tuesday morning beell post...


TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT TUE AUG 27 2013

...TROPICAL WAVES...
TROPICAL WAVE EXTENDS FROM A 1014 MB LOW CENTERED NEAR 10N31W TO
19N29W MOVING W AT 10-15 KT. AS EXPECTED FROM YESTERDAY AT THIS
TIME...THE SOUTHERN VORTICITY MAXIMUM ALONG THE WAVE AXIS BECAME
THE DOMINATE FEATURE AND IS CURRENTLY A WEAK AND BROAD CYCLONIC
MONSOONAL GYRE WITH INFLUENCE FROM 08N-16N BETWEEN 23W-38W. AS
THE LOW-LEVEL ENERGY CONTINUES TO PROPAGATE WESTWARD AS A
WHOLE...UPPER LEVEL SOUTHWESTERLIES TO THE NORTHWEST OF THE WAVE
AXIS WILL SLOWLY FRACTURE ENERGY AWAY FROM THE WAVE TO THE NORTH
OVER THE NEXT 24 TO 48 HOURS.

Interesting forecast. One I may disagree with or at least consider an alternative scenario for now. Upper level southwesterlies do not seem to be a factor with this disturbance. Persistent US east coast/western Atlantic troughing looks strong enough to lift the southern periphery of the A/B ridge to the north allowing the "31N" disturbance (current, updating surface map below) to keep a large part of its gyre intact as it climbs towards 15N. and the central Lesser Antilles.
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Quoting 368. HurricaneHunterJoe:


Is it my imagination or have we had ULL's out the ying yang this year?


Yes more TUTTS than most years.
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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MIAMI FL
1239 PM EDT SUN SEP 1 2013

FLZ071-072-074-172-011715-
COASTAL BROWARD COUNTY FL INLAND BROWARD COUNTY FL METRO BROWARD
COUNTY FL METROPOLITAN MIAMI DADE FL
1239 PM EDT SUN SEP 1 2013

...A SIGNIFICANT WEATHER ADVISORY IS IN EFFECT FOR EASTERN BROWARD
COUNTY...NORTHEASTERN MIAMI-DADE COUNTY...FOR FREQUENT TO EXCESSIVE
LIGHTNING...

* UNTIL 115 PM EDT

* AT 1237 PM EDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
LINE OF STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM OAKLAND
PARK TO MIRAMAR...AND MOVING NORTH AT 10 MPH.

* THE LINE OF STORMS WILL AFFECT...
LAUDERHILL...
POMPANO BEACH...
SOUTHWEST RANCHES...
DAVIE...
NORTH POMPANO BEACH...
INTERSECTION I-75 AND GRIFFIN ROAD...
AND SURROUNDING COMMUNITIES.

THE MAIN IMPACT WILL BE FREQUENT TO EXCESSIVE LIGHTNING. LIGHTNING IS
THE NUMBER ONE WEATHER RELATED KILLER IN FLORIDA. TREES AND OPEN
SHELTERS FOUND IN PARKS...ON BEACHES OR GOLF COURSES OFFER NO
PROTECTION FROM THE DANGERS OF LIGHTNING. SEEK SHELTER IN A SAFE
BUILDING UNTIL THE STORM PASSES.

LAT...LON 2596 8035 2596 8037 2593 8037 2596 8038
2596 8044 2597 8046 2615 8049 2631 8039
2633 8016 2619 8011
TIME...MOT...LOC 1639Z 178DEG 8KT 2621 8017 2596 8038
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Quoting 366. Hurricanes101:


he was being sarcastic




I know just wanted to get that out there :P
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Quoting 326. sunlinepr:
2 ULLs interacting in the area make the forecast difficult....



Is it my imagination or have we had ULL's out the ying yang this year?
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my bet is the coc is around 15n 58w..... this is where the thunderstorms seem to be the most intense and persistent
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Quoting 362. chrisdscane:



you never know Ill still give it a 40% chance overall of developing we'll have to wait and see.


he was being sarcastic
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Quoting 343. Hurricanes101:


How do you know 97L IS NOT THE ONE, as you say? Can you predict the future? If so, can I have a line on the football games next week, I need to make some extra cash
"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"

Rule of thumb 97L is still large and has to take time to consolidate not to mention shear can change on a dime.East caribbean may also disrupt it's development.
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Quoting 351. CybrTeddy:


I have difficulty imaging there wouldn't be northerly winds if we're getting decent amount of westerly winds. Trade winds flow through the Caribbean through the east, leading me to believe these winds we're seeing are indeed a surface circulation of some sort.

Those winds were there yesterday well out in front of the convection from Trinidad eastwards. A broad, elongated slow whoosh of air.
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Thanks for that link, GT. Didn't have that one. ;)




BTW, for you food aficionados, PBS airing:
- New Orleans Food Memories
- New Orleans Restaurants With A Past
- Lost Restaurants of New Orleans
Member Since: July 9, 2006 Posts: 184 Comments: 29610
Quoting 353. KEEPEROFTHEGATE:


naw its a bust nothing is going to form what we are seeing is a figment of our imagination

ya right



you never know Ill still give it a 40% chance overall of developing we'll have to wait and see.
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Navgem wants to develop 97L in the w caribbean and a low behind it north of PR and Hispanola.

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Quoting 352. Gearsts:
Convection warming


Can't quite say that yet; it's getting colder on the eastern end of the invest and it's only been a frame or two anyway. Need a few more to see if it really is in the process of any warming yet.
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A bit off topic....but Southern Cal had the highest PWS in the country a day back? WOW! I live close (4 miles as the crow flies ) to Oak Grove and I got a 15 minute deluge from that storm that dropped 1 1/2"



Tropical Storm Juliette also had churned within 500 miles of San Diego, throwing moist, unstable air toward Southern California just before the system veered sharply to the west and died over the Pacific.

The twin streams of moisture sent the temperature rocketing to 97 degrees in Escondido (9 degrees above normal), and 89 at San Diego's Lindbergh Field (almost 12 degrees above average.) The heat was inescapable; cities as far apart as Encinitas (94 degrees), El Cajon (94), Ramona (94) and Chula Vista (89) baked like french fries left under a heat lamp. The humidity also spiked, reaching 67-percent in places like National City. It's rarely that humid at or near the coast.

Some people also had to dodge thunderstorms. A particularly nasty system erupted at Oak Grove, near Palomar Mountain, dropping 1.5 inches of rain in a short time.

The wild mix caught the attention of scientists at the Scripps Institution of Oceanography in La Jolla, where one researcher sent an inner-office email that said the precipitable water was " just shy of the all-time record for the Miramar site of 2.23" ... set back on August 10, 1998. I believe this is also the highest measured in the U.S. today --substantially higher than places like Key West, FL (1.84") or Corpus Christi, TX (1.73")." The note added that the region also was tapping into moisture from Juliette.

Joe Dandrea, a forecaster at the weather service, said, "We've been close to this level before, but this is the highest PW reading I've seen in the 16 years I've been in San Diego. Ice cream vendors should do really well."
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Meanwhile on Dr. Masters' blog, we all get back to the tropics
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Quoting 352. Gearsts:
Convection warming
with the downcasting though really? just messing, but yes it is. It will most likely continue to do that until DMIN, which is why it is so hard to get this system organized.
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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.

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