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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1055. Patrap
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Quoting 1050. GTstormChaserCaleb:
Day/Night Visible:

awesome contrast on that image
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1053. JRRP
Quoting stormpetrol:


Circulation tightening up and 97L showing signs of ventilating.



I'm putting the LLC at 13.4N/61.7W

mmmm no i do not think so
Link
Member Since: August 16, 2007 Posts: 0 Comments: 6161
1052. JLPR2
I know 97L has a closed circulation, now where exactly is the strongest closed LLC?

Hmm...

I guess anywhere between 62W and 56W. XD There's great cyclonic flow everywhere.

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1051. WoodyFL
Maybe it doesn't have a circulation but it sure looks big. it also looks like some fanning out up to the north.



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Day/Night Visible:

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Quoting 1039. Hurricanes305:
One thing slowing development is the swirl near 14.5N/62W making the it elongated. It will need those to diminish and thing focused closer 60W for development.

For the first time in its so-far short life, 97L actually looks like a reasonable, organized tropical cyclone...inb4 someone says dmin will ruin it...
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Quoting 1036. CybrTeddy:
Expect this wave to get tagged either in the TWO or as an invest before too long: CMC, NAVGEM, FIM8, FIM9, UKMET are all showing something out of it.

wow!!
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Quoting 1043. Tazmanian:




where is that heading


Probably on a similar path to 97L if one believes the UKMET. If one believes the FIM/CMC, it'll go north of the islands.
Member Since: July 8, 2005 Posts: 259 Comments: 24466
Quoting 1024. Gearsts:
I don't think the invest is really that organize as some think.


Why not? Convection has held its own, outflow has improved (due to a developing anticyclone) and a circulation at the surface is tightening up (and closed I might add, albeit broad). The environment is also favorable.

It isn't the best looking system but it certainly appears it is on the brink of becoming a TD.

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Invest 97L is really within a great upper-air setup. The upper-level low that was shearing it yesterday has moved over Hispaniola, allowing for northerly winds to the west of Invest 97L. Meanwhile, a secondary upper-level low is located north of the disturbance, inducing westerly winds north of the system. This is causing anticyclonic flow aloft to develop over 97L.

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1042. Patrap
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Quoting 1023. ILwthrfan:


How fast are the trade winds in the Eastern Caribbean currently compared to climatology?
I have no idea what the climatological norm for trade winds are in the eastern Caribbean; but right now they're 10-15kts which is pretty normal and shouldn't inhibit development. The faster trade wind flow is located north of 20N (20 kts).
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting 1030. belizeit:
we now have a anticyclone over the system


You can clearly see the ventillation it's giving 97L on the satellite images. Quite impressive!

I think this could be the first Hurricane of the season if things keep going as they are. Perhaps even the first major, depending on the track.
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One thing slowing development is the swirl near 14.5N/62W making the it elongated. It will need those to diminish and thing focused closer 60W for development.

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1038. SLU
Quoting 970. nrtiwlnvragn:
Still seems to be multiple low level centers, no well defined one. Barbados is back to North winds.


Link


Back to NW again.

5:00 PM 82.4 °F 94.0 °F 80.6 °F 94% 29.80 in 6.2 mi NW 4.6 mph - N/A Mostly Cloudy

Enough evidence IMO. The only issue today has been to find the exact center but the circulation is closed.
Member Since: July 13, 2006 Posts: 13 Comments: 5355
My educated analysis of 97L: It Looks pretty...lol, hope it keeps this up at d-min.
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Expect this wave to get tagged either in the TWO or as an invest before too long: CMC, NAVGEM, FIM8, FIM9, UKMET are all showing something out of it.
Member Since: July 8, 2005 Posts: 259 Comments: 24466
Quoting 1029. Camille33:

yep
exactly its just this season has sucked and people will love anything they see
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The older GEM run shows a pretty typical path with the system becoming a hurricane and moving through the SE Bahamas and north and then NE staying well offshore the US east coast.
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Member Since: July 21, 2011 Posts: 83 Comments: 7167
1032. JLPR2
Trying to pull itself together east of the Antilles.



Still not quite there...
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Circulation tightening up and 97L showing signs of ventilating.



I'm putting the LLC at 13.4N/61.7W
Member Since: April 29, 2007 Posts: 0 Comments: 8001
we now have a anticyclone over the system
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Quoting 1024. Gearsts:
I don't think the invest is really that organize as some think.

yep
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Quoting 1010. washingtonian115:
If you look closely enough 97L looks like a chicken breast.

Looks Yummy, Crisp-tac-ular
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This is what Oscat was showing
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18z surface analysis.

Member Since: April 29, 2009 Posts: 75 Comments: 14551
1024. Gearsts
I don't think the invest is really that organize as some think.
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Quoting 985. MiamiHurricanes09:
I will say this though, if 97L manages to get into the northwestern Caribbean as an established tropical cyclone, the outcome could be catastrophic.


How fast are the trade winds in the Eastern Caribbean currently compared to climatology?
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Quoting 1008. Tazmanian:



late



the two have it at 40% for the next 48hrs 50% for the next five days
Thank you Taz. Im sorry for the repost. I just saw it on twc and got happy happy that we have something to track. Wishing nothing bad for no one.
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Later, all.
Member Since: October 25, 2005 Posts: 19 Comments: 22563
Quoting 1010. washingtonian115:
If you look closely enough 97L looks like a chicken breast.


Hungry?
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Quoting 991. Seflhurricane:
It is safe to say that we can expect then next TWO to be red and 70-80 Percent


True 60% chance in 48 hours and 80% in 5 days is a good bet.
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Quoting 1012. nrtiwlnvragn:
Fresh off the internets

OFFSHORE WATERS FORECAST FOR THE SW AND TROPICAL N ATLANTIC AND
CARIBBEAN SEA
NWS NATIONAL HURRICANE CENTER MIAMI FL
454 PM EDT SUN SEP 1 2013


Excerpt:

.SYNOPSIS...A TROPICAL WAVE APPROACHING THE YUCATAN PENINSULA
WILL MOVE W OF THE AREA BY TONIGHT. A SECOND TROPICAL WAVE
ACCOMPANIED BY 1012 MB LOW PRES NEAR 16N60W. THE LOW PRES WILL
REACH NEAR 15N64W MON...AS A POSSIBLE TROPICAL CYCLONE...THEN
CONTINUE 15N67W TUE...AND TO 15N73W WED.
16N 60W??? That's different than the best track. Way too far North.
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1017. beell
Meanwhile, what SAL?...


09/01 18Z (click for full image)
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Quoting 1012. nrtiwlnvragn:
Fresh off the internets

OFFSHORE WATERS FORECAST FOR THE SW AND TROPICAL N ATLANTIC AND
CARIBBEAN SEA
NWS NATIONAL HURRICANE CENTER MIAMI FL
454 PM EDT SUN SEP 1 2013


Excerpt:

.SYNOPSIS...A TROPICAL WAVE APPROACHING THE YUCATAN PENINSULA
WILL MOVE W OF THE AREA BY TONIGHT. A SECOND TROPICAL WAVE
ACCOMPANIED BY 1012 MB LOW PRES NEAR 16N60W. THE LOW PRES WILL
REACH NEAR 15N64W MON...AS A POSSIBLE TROPICAL CYCLONE...THEN
CONTINUE 15N67W TUE...AND TO 15N73W WED.

Well south of Hispaniola by Wednesday.

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1015. hydrus
Quoting 1010. washingtonian115:
If you look closely enough 97L looks like a chicken breast.
To bad its not busy out there..I could eat 30 of those..

GOES Imager Cloud Top Pressure
Sep. 01, 2013 - 19:45 UTC
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1014. ncstorm
WPC has 97L heading west into the Yutucan..

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Time to go this evening.... I apologize to my friends if I spoke out of line... But to the one's that po'd me...So be it ...Have a good evening...Going to go listen to Barry McGuire's "Eve of Destruction"
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Fresh off the internets

OFFSHORE WATERS FORECAST FOR THE SW AND TROPICAL N ATLANTIC AND
CARIBBEAN SEA
NWS NATIONAL HURRICANE CENTER MIAMI FL
454 PM EDT SUN SEP 1 2013


Excerpt:

.SYNOPSIS...A TROPICAL WAVE APPROACHING THE YUCATAN PENINSULA
WILL MOVE W OF THE AREA BY TONIGHT. A SECOND TROPICAL WAVE
ACCOMPANIED BY 1012 MB LOW PRES NEAR 16N60W. THE LOW PRES WILL
REACH NEAR 15N64W MON...AS A POSSIBLE TROPICAL CYCLONE...THEN
CONTINUE 15N67W TUE...AND TO 15N73W WED.
Member Since: September 23, 2005 Posts: 14 Comments: 11262
Quoting 1005. wunderkidcayman:

May I remind you that the OSCAT pass was quite a few hours ago
It could be a year old but if you want to use it as evidence of a closed curculation then its gott to show a complete one and not a opened one
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If you look closely enough 97L looks like a chicken breast.
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It's extremely overcast in Barbados, but not a drop of rain
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Quoting 1002. GatorWX:
I see 97 is holding its own from my phone, trying to get stacked, waiting for dMAX.



No time to check the stats.

See ya when I get back.
is it getting the banding feature? Sure looks like it
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1006. JRRP
Quoting DonnieBwkGA:
Waiting for the GEM to run. It seems stuck.

so you will wait the 00z run
Member Since: August 16, 2007 Posts: 0 Comments: 6161
Quoting 998. belizeit:
That Oscat pass that was shown is clearly showing the system is elongated and opened to the W just as NHC mentioned in there TWO

May I remind you that the OSCAT pass was quite a few hours ago
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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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