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 1997. Astrometeor:


I thought about saying something about his college being special, but it didn't sound right. Better to say he still has to learn then get a free day altogether. Now, most schools (regardless of level) are off tomorrow, including mine, but I still have homework to do.

Looked at the U of Miami and FAU and they're both off as well but didn't want to post it either.
Member Since: September 30, 2008 Posts: 0 Comments: 108
2004. JRRP
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Quoting 1968. moonlightcowboy:


Red, I appreciate your enthusiasm for an annular system, but 97L is anything but annular. Sorry.


I base my annular concerns on 1. persistence. 2. The donut ring presentation when there is one llc, which happened earlier yesteday, and maybe today (I was gone) 3. Wind field symmetry very tight with large footprint. 4. 'Innoculation' from destructive conditions.
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Wouldn't it just follow the 1200 millibar line.?
Quoting GTstormChaserCaleb:
I'll go out on a limb and say that Tropical Wave approaching 55 West will catch up to 97L and help move it to start moving again towards the wnw.

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2001. sar2401
Quoting opal92nwf:

I'm confused. I must have my terms mixed up. I know that it's the time like now when the sun has gone down and it makes the thunderstorms weaken.

No, it's the opposite. From now until about an hour before sunrise the thunderstorms usually grow because the differential between the air temperatures and the water temperatures are small, or the water is actually warmer than the air. Now the air near the surface which is in contact with the water warms by conduction, and then begin to rise, so thunderstorms grow. Tropical storms not expanding at night is not a good sign for longevity.
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Quoting 1990. JRRP:
Ryan Maue ‏@RyanMaue 5h
Good news, GFS is back from the dead -- anomaly correlation scores for NHemi back above 0.8
This post says it all on how much the GFS has struggled since the upgrade. I mean you have models like the NAVGEM, UKMET, and CMC outperforming it? C'mon now. I'm really disappointed and upset about this.
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Quoting 1997. Astrometeor:


I thought about saying something about his college being special, but it didn't sound right. Better to say he still has to learn then get a free day altogether. Now, most schools (regardless of level) are off tomorrow, including mine, but I still have homework to do.

Yep, me too "sigh" "summer where did you go!"
Member Since: May 12, 2012 Posts: 11 Comments: 2875
1998. JLPR2
Quoting 1986. opal92nwf:

I'm confused. I must have my terms mixed up. I know that it's the time like now when the sun has gone down and it makes the thunderstorms weaken.


Once the sun sets D-min ends and D-max begins since without the Sun the air starts to cool, it peaks right before/or at sunrise.

The opposite is true for D-min, once the sun rises the air begins to warm and so during the day we are at D-min until it peaks at sunset.
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Quoting 1978. opal92nwf:

My college has off tomorrow....


I thought about saying something about his college being special, but it didn't sound right. Better to say he still has to learn then get a free day altogether. Now, most schools (regardless of level) are off tomorrow, including mine, but I still have homework to do.
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Quoting 1988. daddyjames:

Agree with you. The Euro and the GFS now are showing this elongated wave splitting into two - much like the NHC forecast. Half of it moving north of PR, the other hal south of Hispanolia. Much like described in the last NHC TWDAT. Question is, which one eventually develops?


NHC was laying odds on the southern one before. Will be interesting if they change their tune.

and why not either both or neither? I would hedge my bets on the southern one though. Just seems the most likely of the two.
Member Since: September 30, 2008 Posts: 0 Comments: 108
Well, here we go again. It's so much fun during the hurricane season when we have a storm (whether it be an invest or a hurricane!) out there and you go to bed and then wake up and so much has happened with that system.
Member Since: May 12, 2012 Posts: 11 Comments: 2875
Quoting 1982. scottsvb:


What do you expect out over 2 weeks?
No it's not even that man, just track the low level vorticity and you will see what I mean, I would have expected by that time the system either getting absorbed by a trough pushing off the East Coast and going OTS or making landfall already. It's common sense man, the atmosphere doesn't move that slow. We need to think what makes meteorological sense, and the GFS model is not making sense here of late. Remember what it did with 97L before it emerged off the coast of Africa last week, it strengthened it quite quickly withing the 3-5 day window, that never happened. I'm sorry for those who sit here and worship the GFS model, but it has been off, and you're ignorant if you can't see that.
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Quoting 1985. GTstormChaserCaleb:
I'll go out on a limb and say that Tropical Wave approaching 55 West will catch up to 97L and help move it to start moving again towards the wnw.


Yeah, I really don't understand this stall 97l is doing now.
Member Since: May 12, 2012 Posts: 11 Comments: 2875
1991. Relix
What a mess going on there. Tomorrow should be fun!
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1990. JRRP
Ryan Maue ‏@RyanMaue 5h
Good news, GFS is back from the dead -- anomaly correlation scores for NHemi back above 0.8
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I think I see a center developing S of 15N N of Barbados I'm going to wait and watch it for a few hours see what it does then reconfirm this also the radar also pick up this though it is very weak and if your not lookin close enough you probably miss it
Member Since: June 13, 2009 Posts: 2 Comments: 12716
Quoting 1963. redwagon:


That is a storm cracking in two. Like Debby did in the GOM. One goes W, the other to FL. I CANNOT find yet the image I posted last night of annular Isabel 2003 that had 6 centers at her peak, the oblique shot really showed them off.

Agree with you. The Euro and the GFS now are showing this elongated wave splitting into two - much like the NHC forecast. Half of it moving north of PR, the other half south of Hispanolia. Much like described in the last NHC TWDAT. Question is, which one eventually develops?


NHC was laying odds on the southern one before. Will be interesting if they change their tune.
Member Since: June 25, 2011 Posts: 2 Comments: 3733
1987. scott39
Quoting 1966. moonlightcowboy:


I saw the vorticity chart, but IDK what time they chart those things, but I'm thinking the updated won't look that good even. This thing looks as bad as I've seen it.
Im looking at the 0300am for 9/2. It looks better than the 0000am 9/2. Not much but still better.
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Quoting 1969. JLPR2:


Nah... it's late and it's Sunday, was Saturday a moment ago. xD

Also, actually we are in D-max, we haven't peaked yet, but definitely D-max.

I'm confused. I must have my terms mixed up. I know that it's the time like now when the sun has gone down and it makes the thunderstorms weaken.
Member Since: May 12, 2012 Posts: 11 Comments: 2875
I'll go out on a limb and say that Tropical Wave approaching 55 West will catch up to 97L and help move it to start moving again towards the wnw.

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Quoting 1962. GTstormChaserCaleb:
There is something seriously wrong with the GFS model man, it's not going to take 97L or that wave behind it 384 hrs. to reach the Mid-Atlantic states.

Link


Given how much the gfs has struggled this season, I agree that there is probably something wrong with the model. If this sort of unrealistic forecasts were an exception, I'd just discard this run. But, I think the NWS needs to take a look at the GFS and perhaps need to work on another upgrade, because this 'new and improved' GFS has not been performing up to the level expected.
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Good night, see u tomorrow for another crazy day XD
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Quoting 1962. GTstormChaserCaleb:
There is something seriously wrong with the GFS model man, it's not going to take 97L or that wave behind it 384 hrs. to reach the Mid-Atlantic states.

Link


What do you expect out over 2 weeks?
Member Since: January 22, 2006 Posts: 0 Comments: 1723
Quoting 1924. hurricanes2018:
nice tropical wave with t.storm on land here looking better then invest 97L WITH no rain with it!


Could use some more spin...but not bad...

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Quoting 1974. MiamiHurricanes09:
You may want to look at the 2005 archived advisories and think of it as the present.


Funny XD

Done that many times before
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1979. JRRP
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Quoting 1973. Astrometeor:


It's a Labor Day for workers, not for educators and students. Education never stops.

My college has off tomorrow....
Member Since: May 12, 2012 Posts: 11 Comments: 2875
1977. scott39
97L is in no worse shape than it was 12 hours ago. In fact the vorticity levels look better. The LLC is still elongated, but slowly coming together. DMAX will give 97L what it needs for continued development.
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Quoting 1967. MiamiHurricanes09:
Why is anyone even surprised that 97L looks like absolute crap at the moment lol? Absolutely no surface convergence and poor divergent flow aloft will do that to systems with ill-defined circulation...especially at the diurnal minimum.

The wave behind 97L may be gearing up to fire some decent thunderstorm activity over the next few hours from the look of the newer maps though.

I was just trying to feel/test the mood of the blog. I know it's diurnal minimum. Don't get me wrong, even though I think 97l looks like crap at the moment I still have high hopes for it.
Member Since: May 12, 2012 Posts: 11 Comments: 2875
I would also like someone to try to lend an explanation for this.They have influenced our weather hear in S.Fl. Mayby Levi has an answer?
Quoting GTstormChaserCaleb:
There have been so many ULL's this year, what is the cause for so many of these ULL's?

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Quoting 1970. CaribBoy:
I want MEGA RI

Lol
You may want to look at the 2005 archived advisories and think of it as the present.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting 1959. Bluestorm5:
Yeah, I was really worn out from the week and I got school tomorrow (my college isn't aware of holiday I guess...) so I did my homework yesterday and relaxed today. My homework load isn't heavy right now but it will get so soon.


It's a Labor Day for workers, not for educators and students. Education never stops.
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Whoaaa GFS hurricane bound for the Mid Atlantic. Not okay.

Total fantasyland thankfully.
Member Since: August 28, 2008 Posts: 79 Comments: 3714
Quoting 1968. moonlightcowboy:


Red, I appreciate your enthusiasm for an annular system, but 97L is anything but annular. Sorry.


LOL
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I want MEGA RI

Lol
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1969. JLPR2
Quoting 1957. opal92nwf:
I take it that the reason everyone is so calm on here despite 97L looking like crap at the moment is because we know it's Dmin?


Nah... it's late and it's Sunday, was Saturday a moment ago. xD

Also, actually we are in D-max, we haven't peaked yet, but definitely D-max.
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Quoting 1963. redwagon:


That is a storm cracking in two. Like Debby did in the GOM. One goes W, the other to FL. I CANNOT find yet the image I posted last night of annular Isabel 2003 that had 6 centers at her peak, the oblique shot really showed them off.


Red, I appreciate your enthusiasm for an annular system, but 97L is anything but annular. Sorry.
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Why is anyone even surprised that 97L looks like absolute crap at the moment lol? Absolutely no surface convergence and poor divergent flow aloft will do that to systems with ill-defined circulations...especially at the diurnal minimum.

The wave behind 97L may be gearing up to fire some decent thunderstorm activity over the next few hours from the look of the newer maps though.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting 1956. scott39:
Vorticity looks a little better at the 500mb level.


I saw the vorticity chart, but IDK what time they chart those things, but I'm thinking the updated won't look that good even. This thing looks as bad as I've seen it.
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1965. scott39
For now low level convergence isnt happening with 97L. NW models more than likely will be a bust.
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Quoting 1955. wunderkidcayman:

Yes I agree



I also agree. It is breaking up now which will allow it to move furhter W than the models are currently showing. That could be a problem, but we can not know at this time. There is just not enough circulation for the modles to rely on.
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Quoting 1937. JLPR2:


OSCAT caught part of the broad spin of the TW behind 97L, pretty far south.


That is a storm cracking in two. Like Debby did in the GOM. One goes W, the other to FL. I CANNOT find yet the image I posted last night of annular Isabel 2003 that had 6 centers at her peak, the oblique shot really showed them off.
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There is something seriously wrong with the GFS model man, it's not going to take 97L or that wave behind it 384 hrs. to reach the Mid-Atlantic states.

Link
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1961. beell
Quoting 1952. moonlightcowboy:


Going towards dmax sure doesn't seem to be helping it any. Looking fairly puny.


I think the dry air did a dagger-to-the-heart thing. It still looks better than me!

I think it's time to give it a rest. See ya later, mlc.
:)
Member Since: September 11, 2007 Posts: 145 Comments: 16920
Quoting 1930. Maineweatherguy20023:

hmm-do you think there will be a hurricaneless season in the future?
No, though current aspiring meteorologists in high school/college like myself may contend with less active hurricane seasons in the future during the pinnacle of our careers relating to the theory of the Atlantic Multidecadal Oscillation. Also, we're still not really sure how AGW will impact storms of the future. 
Member Since: August 28, 2008 Posts: 79 Comments: 3714
Quoting 1953. GTstormChaserCaleb:
No don't say that it was a good blog, you're in University dude, so you have other assignments that is more important than this blog to complete. Right now I'm procrastinating and have a paper that is due on Wed. not really hard just 1 page, but I also would like to get started on Calculus, so I get ahead in that class, cause my fear is to fall behind and dig myself into a hole which I cannot afford.
Yeah, I was really worn out from the week and I got school tomorrow (my college isn't aware of holiday I guess...) so I did my homework yesterday and relaxed today. My homework load isn't heavy right now but it will get so soon.
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Quoting 1955. wunderkidcayman:

Yes I agree


It will not. The system will merge with 2 energies and eighter way is not a caribbean cruiser. The weakness by day 5 will be capable of recurving this north.
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I take it that the reason everyone is so calm on here despite 97L looking like crap at the moment is because we know it's Dmin?
Member Since: May 12, 2012 Posts: 11 Comments: 2875
1956. scott39
Quoting 1952. moonlightcowboy:


Going towards dmax sure doesn't seem to be helping it any. Looking fairly puny.
Vorticity looks a little better at the 500mb level.
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Quoting 1947. scott39:
97L will have to do some amazing development in the next 24 to 36 hours to go N of the Islands. Its going to be a Caribbean cruiser and a possible GOM Beast!

Yes I agree

Member Since: June 13, 2009 Posts: 2 Comments: 12716

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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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