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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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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354. beell
Quoting 323. Levi32:
The equatorial inflow into 97L isn't very moist, but it isn't terribly dry either. It appears that the low-level structure extends up to ~850mb, above which the easterly trade wind flow resumes. We will have to see if this layer of westerlies deepens with time.

12z sounding out of Barbados.



97L brought this monsoonal gyre and "anomalous" low-level westerlies from the central Atlantic. I think they are to remain with this system for the duration. Certainly a kick-start/head-start for development
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Quoting 346. chrisdscane:




many islands reporting west winds, this is ramping up pretty quickly.


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

ya right
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Convection warming
Member Since: August 2, 2010 Posts: 0 Comments: 1804
Quoting 299. scottsvb:



Peeps, everyone knows and can see there are West winds... What we need to find is North winds and not 250 miles away from the middle of the elongated center. If there are N winds around 15N and 57-59W then we might have something if it can keep T-Storms going into and through the night.


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.
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Quoting 321. Tazmanian:
IN TERMS OF ACCUMULATED CYCLONE ENERGY...WHICH MEASURES THE COMBINED
STRENGTH AND DURATION OF TROPICAL STORMS AND HURRICANES...TROPICAL
CYCLONE ACTIVITY THROUGH THE END OF AUGUST WAS ABOUT 70 PERCENT
BELOW
THE 1981-2010 AVERAGE.


My god. :| Even 2009 was above August average!
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348. wpb
000
NOUS42 KNHC 011535
REPRPD
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1100 AM EDT SUN 01 SEPTEMBER 2013
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 02/1100Z TO 03/1100Z SEPTEMBER 2013
TCPOD NUMBER.....13-092

I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY: POSSIBLE LOW-LEVEL INVEST OF
CENTRAL CARIBBEAN SYSTEM NEAR 15.0N 72.0W FOR 03/1800Z.
3. REMARK: THE NASA 871 GLOBAL HAWK MAY FLY A 24-HOUR RESEARCH
MISSION OVER THE CARIBBEAN SYSTEM...TAKING OFF AT
03/1100Z.

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Quoting 211. Walshy:
GaWx from AmericanWx

10 Strongest MJO phase 1, 2 peaks during 8/21-9/20 since 1975: TC geneses when MJO 1.50 in phase 1 or 2 that later became H%u2019s

-3.08 peak 8/28/79: cat 5 David, cat. 4 Frederic, cat 2 Gloria
-2.21 peak 9/5/81: cat 1 Emily, cat 3 Floyd, cat 2 Gert
-2.07 peak 9/19/89: none
-2.01 peak 9/4/83: cat 1 Chantal
-2.01 peak 9/20/04: cat 1 Lisa
-1.98 peak 8/23/99: cat 2 Dennis
-1.92 peak 8/26/11: none
-1.90 peak 8/29/07: cat 5 Felix
-1.89 peak 8/30/88: cat 1 Debby
-1.88 peak 8/23/08: cat 4 Gustav

So, there were geneses of TC%u2019s during these 10 strongest amplitude periods in phases 1 and 2 that later became 12 H%u2019s (5 major) and these resulted in TC%u2019s during 8 of the 10 periods that later became H%u2019s.
Three hit the US as a H, two of them being major H hits.

Since all of these storms occur in late August or September, I'm not sure about the significance of the MJO. This is near the peak of hurricane season. Literature I've seen indicated no MJO effects detected in the MDR of the Atlantic. GOM, yes. (Can't find that link at the moment.) But check out "A Global View of Equatorial Waves and Tropical Cyclogenesis".

"The MJO variance was weaker in the Western Hemisphere than in the Eastern Hemisphere (Figs. 6e and 7e). Even with the 2 mm day threshold, only 5% of Atlantic storms were attributed to the MJO (Fig. 5c)"

So they relaxed their criteria for attribution to get 5%. That sounds like an upper bound.
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many islands reporting west winds, this is ramping up pretty quickly.
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Quoting 338. Patrap:
Annoying is those who are quoting the idiocy.
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Quoting 314. washingtonian115:
"we cant have a major hurricane or a storm that causes a lot of problems before the season is out " .Problem is 97L is just not the one.Yeah I already know that same tired rule of "it only takes one".But 97L IS not the one.And it's chances of developing at the present are low.It still has the east caribbean to go through which is not very conductive of cyclone development.Even the good Doc says that.


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
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Quoting 330. KEEPEROFTHEGATE:
doc said 97L is a threat to dev into a storm says so right in the blog header unless he posts a different header for me than anyone else
"It still has the east caribbean to go through which is not very conductive of cyclone development.Even the good Doc says that"
. 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

:).
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Its simple then, place my name on your ignore list and you wont have to listen to accurate forecasts.
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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.
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97L is looking more organized as the morning goes on and appears to have the potential to become a cyclone fairly soon. It will need to do so before it reaches the area of the Caribbean between Hispanola and S America. If it does not develop by then it usually will not for systems that enter the Caribbean from the east.
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Annoying is those who are quoting the idiocy.
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Again It's Really Interesting that 96L Too is also doing quite well to get its act together...it too has been firing more deep convection with a way better defined spin and circulation at the mid and lower levels (compared to 97L).
Re: 96L -There should be no doubt here of a closed off low level center of circulation. The NHC May have written it off with Lower percentage probablities a tad too early & Forcaster Stewart et Al. IMO...

Perhaps the MJO etc. may cause things to Really heat up a bit for September...
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Quoting 333. southernstorm:
I don't have a dog in the fight but if you forecast in the moment it isn't forecasting, right? Forecasting is about the coming days, right? You are very annoying.



put him on ignore then
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Levi Cowan ‏@TropicalTidbits 1 min
12z Barbados sounding shows moderate moisture within equatorial inflow. Layer of southwesterlies extends to 850mb.

Link
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the gfs has done a vary poor job this season
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Quoting 281. SuperStorm093:


Keep it going, VRL just agreed with what I said. Its not called downcasting, its called reality. I forecast in the moment and not in the next coming days. That is how I do it, if I see it becoming organized then I will be good. But you guys have been wishcasting all year and hasnt worked out now has it?
I don't have a dog in the fight but if you forecast in the moment it isn't forecasting, right? Forecasting is about the coming days, right? You are very annoying.
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Quoting 313. Sfloridacat5:
Amazed that the 12Z GFS doesn't show anything at all for 97L.
I'm not it has had initialization issues this year. Surface charts already have it as a low pressure area. I think that some of us might be licking our chops hoping the GFS fails to see 97L turn into a tropical system, so that we can prove a point, which is models are only their for guidance and do not reflect the actual outcome nor should they be taken as gospel, we have seen too many times this year and in years past where some models have completely missed the developing system. If your starting point is off then your ending point will be off as well. This goes back to Physics 101 when talking about trial-and-error.
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also if anyone cares GFS for now up to 10 runs shows the CV season going by mid september. despite the slow start dont be shocked if we get a few late season CV hurricanes
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Quoting 314. washingtonian115:
"we cant have a major hurricane or a storm that causes a lot of problems before the season is out " .Problem is 97L is just not the one.Yeah I already know that same tired rule of "it only takes one".But 97L IS not the one.And it's chances of developing at the present are low.It still has the east caribbean to go through which is not very conductive of cyclone development.Even the good Doc says that.
doc said 97L is a threat to dev into a storm by wed or thur says so right in the blog header unless he posts a different header for me than anyone else
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Quoting 323. Levi32:
The equatorial inflow into 97L isn't very moist, but it isn't terribly dry either. It appears that the low-level structure extends up to ~850mb, above which the easterly trade wind flow resumes. We will have to see if this layer of westerlies deepens with time.

if 97L takes a southern track towards the NW caribbean, how does the environment look to be around say 5-7 days? lots of heat content south of cuba. possible sleeper system?
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MONTHLY TROPICAL WEATHER SUMMARY
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM PDT SUN SEP 01 2013

FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

OVERALL TROPICAL CYCLONE ACTIVITY IN THE EASTERN NORTH PACIFIC BASIN
DURING AUGUST WAS BELOW AVERAGE. ALTHOUGH FOUR TROPICAL CYCLONES
FORMED...ONLY ONE OF THESE...HENRIETTE...REACHED HURRICANE
STRENGTH. THERE HAVE BEEN NO MAJOR HURRICANES IN THE EASTERN NORTH
PACIFIC BASIN SO FAR THIS SEASON. BASED ON A 30-YEAR CLIMATOLOGY
FROM 1981 TO 2010...THREE TO FOUR NAMED STORMS DEVELOP ON AVERAGE
IN THE BASIN DURING AUGUST...WITH TWO BECOMING HURRICANES AND ONE
REACHING MAJOR HURRICANE STRENGTH.

IN TERMS OF ACCUMULATED CYCLONE ENERGY...WHICH MEASURES THE COMBINED
STRENGTH AND DURATION OF TROPICAL STORMS AND HURRICANES...TROPICAL
CYCLONE ACTIVITY SO FAR THIS YEAR IS ABOUT 40 PERCENT BELOW NORMAL.

REPORTS ON INDIVIDUAL CYCLONES...WHEN COMPLETED...ARE AT THE WEB
SITE OF THE NATIONAL HURRICANE CENTER...USE LOWER-CASE LETTERS...
WWW.HURRICANES.GOV/2013EPAC.SHTML

SUMMARY TABLE

NAME DATES MAX WIND (MPH)
------------------------------------------------- --
TS ALVIN* 15-17 MAY 60
H BARBARA* 28-30 MAY 80
H COSME 23-27 JUN 85
H DALILA 30 JUN-7 JUL 75
H ERICK* 4-9 JUL 80
TS FLOSSIE 25-30 JUL 70
H GIL 30 JUL-6 AUG 85
H HENRIETTE 3-11 AUG 105
TS IVO 22-25 AUG 45
TS JULIETTE 28-29 AUG 50
TS KIKO 31 AUG- 70
------------------------------------------------- --

* DENOTES A STORM FOR WHICH THE POST-STORM ANALYSIS IS COMPLETE.

$$
HURRICANE SPECIALIST UNIT

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2 ULLs interacting in the area make the forecast difficult....

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Quoting 268. Levi32:
So indeed, most of the global models have failed miserably on the representation of 97L today, and have underestimated its organization. That should not come as a surprise to anybody given the type of wave this is.
Type of wave? ?
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I don't understand why everybody insists on speaking in absolutes with Invest 97L or the season in general. We don't know for sure how either will end up.
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The equatorial inflow into 97L isn't very moist, but it isn't terribly dry either. It appears that the low-level structure extends up to ~850mb, above which the easterly trade wind flow resumes. We will have to see if this layer of westerlies deepens with time.

12z sounding out of Barbados.

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97L
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MONTHLY TROPICAL WEATHER SUMMARY
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT SUN SEP 01 2013

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

TROPICAL CYCLONE ACTIVITY IN THE NORTH ATLANTIC BASIN IN AUGUST
WAS BELOW AVERAGE...WITH ONLY TWO TROPICAL STORMS FORMING. BASED
ON A 30-YEAR (1981-2010) CLIMATOLOGY...THREE OR FOUR NAMED STORMS
FORM ON AVERAGE IN THE ATLANTIC BASIN IN AUGUST...WITH ONE OR TWO
BECOMING HURRICANES.

IN TERMS OF ACCUMULATED CYCLONE ENERGY...WHICH MEASURES THE COMBINED
STRENGTH AND DURATION OF TROPICAL STORMS AND HURRICANES...TROPICAL
CYCLONE ACTIVITY THROUGH THE END OF AUGUST WAS ABOUT 70 PERCENT
BELOW THE 1981-2010 AVERAGE.

REPORTS ON INDIVIDUAL CYCLONES...WHEN COMPLETED...ARE AT THE WEB
SITE OF THE NATIONAL HURRICANE CENTER...USE LOWER-CASE LETTERS...
WWW.HURRICANES.GOV/2013ATLAN.SHTML

SUMMARY TABLE

NAME DATES MAX WIND (MPH)
------------------------------------------------- --
TS ANDREA* 5-7 JUN 65
TS BARRY 17-20 JUN 45
TS CHANTAL 8-10 JUL 65
TS DORIAN 24 JUL-3 AUG 60
TS ERIN 15-18 AUG 40
TS FERNAND 25-26 AUG 50
------------------------------------------------- --

* DENOTES A STORM FOR WHICH THE POST-STORM ANALYSIS IS COMPLETE.

$$
HURRICANE SPECIALIST UNIT

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Quoting 316. Doppler22:
I am a little concerned that people are getting security flags because a virus was posted but I haven't gotten any

I haven't gotten any either. I run Firefox.
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ULL moving W fast... Interesting clash of variables....
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Quoting 302. Sfloridacat5:


Definitely looks like it trying to spin up. What concerns me is the wind shear blowing the top of the convection off to the north.


Winds shear is not much of a problem anymore. The ULL is ventilating the system. Thanks to the heat being released from the convection wind shear over the LLC has dropped to 5-15kts.

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Quoting 279. TropicalAnalystwx13:

Or maybe not so clear.



*smirks
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I am a little concerned that people are getting security flags because a virus was posted but I haven't gotten any
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Quoting 294. whitewabit:
what I said one post today and everyone started saying downcast lol.
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"we cant have a major hurricane or a storm that causes a lot of problems before the season is out " .Problem is 97L is just not the one.Yeah I already know that same tired rule of "it only takes one".But 97L IS not the one.And it's chances of developing at the present are low.It still has the east caribbean to go through which is not very conductive of cyclone development.Even the good Doc says that.
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Amazed that the 12Z GFS doesn't show anything at all for 97L.
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Quoting 194. Tazmanian:



30% next 48hrs 70% the next 5 days


sounds about right...
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291. SuperStorm093 4:33 PM GMT on September 01, 2013

Because those people have a reputation on this blog as those who show objectivity. In other words, they do not downcast everything and the certainly do not push their agendas on everyone else. Most important of all, they do not act all holier than thou and pat themselves on the back like some ego-driven Narcissist.
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Quoting 225. Dakster:
Who posted a virus/Trojan? I am getting security flags from the site now.


I am getting security flags from mi smarthphone too.
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Quoting 299. scottsvb:



Peeps, everyone knows and can see there are West winds... What we need to find is North winds and not 250 miles away from the middle of the elongated center. If there are N winds around 15N and 57-59W then we might have something if it can keep T-Storms going into and through the night.


I feel the same, seems pretty stretched still, evident on satellite as well.
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308. JRRP
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307. whitewabit (Mod)
Quoting 295. KEEPEROFTHEGATE:
trying to fine it taz not sure which one it is


Keep its in the last 50 posts somewhere ..
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Quoting 303. unknowncomic:
It looks like the GFS has 97L going over Hispanola, and that is one reason it does not develop it.



seems like the gfs is a outliner
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I see, blog has something to track and will be happy, at least unless havoc is looming (hope not!, though I'm suspicious 97L will mean no good down the road). So no need for me to fill in with European weather for a while, unless something really dramatic is happening. And a busy week for me in office lies ahead anyway.

I'll follow your fate over there, and whish you a nice Sunday from intermittently quite chilly Germany as a trough from the UK is moving in:

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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.