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 2039. GTstormChaserCaleb:
I do remember you stating that earlier in the season and currently that is what is going on as we have this persistent trough off the East Coast. By the way I wasn't jumping on Scottsvb I'm just really frustrated with the models right now, even in the short range which shows development and a strengthening system one run only for the next run to kill it off completely. It really does come down to nowcasting now and a good look at the surface charts, and cimss products, along with the actual satellite imagery.


bro, I never look at just one run on any model....I only look at a persistent run of all the models. I look at the consensus of them all to even try to determine anything. Seems the NHC does much the same although, they do have their favorite models more than others I do believe.
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Quoting 2048. JRRP:

that is from 12z


Only one I can get access for the ECMWF to compare at the moment.

0Z on the GFS is showing this still, but developing the vorticity to the North of Puerto Rico.
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2053. scott39
Quoting 2047. TampaSpin:
I hate to even post this GFS current run at 384hrs out...but it shows a Carolina system from 97L


from 97L?
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2052. Gearsts
Not getting better organize
Member Since: August 2, 2010 Posts: 0 Comments: 1578
2051. scott39
Quoting 2045. RGVtropicalWx13:

I WASN'T speaking vorticity wise just convection. Besides the NHC says this has a shot in BOC in a few days. Just remember last weekend when a blogger say Fernand would form in the BOC and you said it wouldn't? Well look what happen then. Same thing tonight as last week. I'm NOT saying this is gonna form NOW. But in the BOC it HAS a shot develop.
BOC can spin up some quick.
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2050. JRRP
Quoting Gearsts:
All the models taking it north over us

yeah
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Quoting 2046. GTstormChaserCaleb:
You can see the TW I'm talking about approaching 97L on shortwave imagery.


Yeah, it should help with moisture
Member Since: May 12, 2012 Posts: 11 Comments: 2394
2048. JRRP
Quoting daddyjames:
At 72 hours:
GFS


ECMWF


Shows the Vorticity being cut in half by the Greater Antilles. Currently both models develop the northern portion - that north of PR

that is from 12z
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I hate to even post this GFS current run at 384hrs out...but it shows a Carolina system from 97L


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You can see the TW I'm talking about approaching 97L on shortwave imagery.

Member Since: June 30, 2013 Posts: 11 Comments: 7698
Quoting 2028. TampaSpin:



NOPE ...no Vorticity there at all....purely Divergence....it will fade soon.

I WASN'T speaking vorticity wise just convection. Besides the NHC says this has a shot in BOC in a few days. Just remember last weekend when a blogger say Fernand would form in the BOC and you said it wouldn't? Well look what happen then. Same thing tonight as last week. I'm NOT saying this is gonna form NOW. But in the BOC it HAS a shot develop.
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New YouTube Tropical Weather Discussion:

Link
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Quoting 2039. GTstormChaserCaleb:
I do remember you stating that earlier in the season and currently that is what is going on as we have this persistent trough off the East Coast. By the way I wasn't jumping on Scottsvb I'm just really frustrated with the models right now, even in the short range which shows development and a strengthening system one run only for the next run to kill it off completely. It really does come down to nowcasting now and a good look at the surface charts, and cimss products, along with the actual satellite imagery.

did you find 500 mb model avgs ?
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2042. Gearsts
Quoting 2004. JRRP:
All the models taking it north over us
Member Since: August 2, 2010 Posts: 0 Comments: 1578
Quoting 2026. Bluestorm5:
I really don't trust any models right now. I know it's still an invest, but it's nowcasting time even though it's early. Also, East Caribbean isn't going to let storm develops until Jamaica area so we would have to be patient.

How long do you think it will take to get to Jamaica?
2-3 days?
Member Since: May 12, 2012 Posts: 11 Comments: 2394
2040. scott39
Quoting 2026. Bluestorm5:
I really don't trust any models right now. I know it's still an invest, but it's nowcasting time even though it's early. Also, East Caribbean isn't going to let storm develops until Jamaica area so we would have to be patient.
People start to loose interest quickly when they dont see thunderstorms blooming like the 4th of July. Its all about the dance when tracking an Invest. Yes, 97L needs thunderstorms. Does it mean the dance is over? Of course not. Learning more about the development of a TC will help everyone know when to quit or keep dancing.
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Quoting 2036. TampaSpin:



ULL's come off the tails of troughs in between Highs and Low's that break of the tails. Once started they can spin for many days until they unwind. We have had as I have noted many fronts this year. I am one that believes that the early sign of an early winter in the Artic was the sign of an average season in the tropics. I noted that in my blog the first week in August.
I do remember you stating that earlier in the season and currently that is what is going on as we have this persistent trough off the East Coast. By the way I wasn't jumping on Scottsvb I'm just really frustrated with the models right now, even in the short range which shows development and a strengthening system one run only for the next run to kill it off completely. It really does come down to nowcasting now and a good look at the surface charts, and cimss products, along with the actual satellite imagery.
Member Since: June 30, 2013 Posts: 11 Comments: 7698
At 72 hours:
GFS


ECMWF


Shows the Vorticity being cut in half by the Greater Antilles. Currently both models develop the northern portion - that north of PR
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Hurricane Ophelia is my poster-child for the 2013 Atlantic Hurricane Season, what's yours?

What a beauty
Member Since: May 12, 2012 Posts: 11 Comments: 2394
Quoting 2019. opal92nwf:

I remember in one of Levi's tidbits in the beginning of the season he was saying that there were going to be a lot of ULL and he explained why. I think they were breaking off of troughs or something?



ULL's come off the tails of troughs in between Highs and Low's that break of the tails. Once started they can spin for many days until they unwind. We have had as I have noted many fronts this year. I am one that believes that the early sign of an early winter in the Artic was the sign of an average season in the tropics. I noted that in my blog the first week in August.
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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.


Busy work with lots of homework is nothing odd for meteorology majors, I'm booked, meteorology is my life right now, and I'm not bothered by it :)

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And in other news...

Peru: Six Killed in Heavy Snowstorm

September 1, 2013

A late-winter snowstorm is has now killed 6 people and more than 30,000 domestic animals in southern Peru and promted a declaration of a state of emergency.
Link
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2033. sar2401
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.


That's a pretty long limb. :-) When that wave catches up, it will be weak, and only serve to draw more dry air into the combined circulation. I think 97L will swallow it whole and nothing will happen. The forces that are keeping it stationary now are not going to be changed by a weak wave.
Member Since: October 2, 2004 Posts: 0 Comments: 13464
Quoting 2031. hurricanes2018:
I do not see anything happern to invest 97L RIGHT NOW and did you see what happern to invest 96L DIE OUT TO

did you see tim tebow got cut right now!
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Quoting 2026. Bluestorm5:
I really don't trust any models right now. I know it's still an invest, but it's nowcasting time even though it's early. Also, East Caribbean isn't going to let storm develops until Jamaica area so we would have to be patient.
I do not see anything happern to invest 97L RIGHT NOW and did you see what happern to invest 96L DIE OUT TO
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Quoting 2008. sar2401:

I think several of us said it was a bad idea to change it over to the supercomputer during hurricane season. This seems to bear out that prediction. Do software and hardware upgrades at non-critical times.
The thing you would want to see is either show no development and it pans out or show development and that pans out, don't go ghost on us only to try and show it again, I hardly call that an improvement, maybe give it some time this season, and next year it will do better.
Member Since: June 30, 2013 Posts: 11 Comments: 7698

Quoting 2026. Bluestorm5:
I really don't trust any models right now. I know it's still an invest, but it's nowcasting time even though it's early. Also, East Caribbean isn't going to let storm develops until Jamaica area so we would have to be patient.
I agree, blog needs to stop jumping on the doomsday predictions, little early for that stuff. 
Member Since: August 28, 2008 Posts: 79 Comments: 3486
Quoting 2011. RGVtropicalWx13:
Hmm pre-98L in the nw Caribbean looks decent right now. I'm sure it has a shot. Mexico OR Not.



NOPE ...no Vorticity there at all....purely Divergence....it will fade soon.
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right now no more invest 96L die out with t.storms and rain now invest 97L DIE OUT TONIGHT..this is crazy!
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I really don't trust any models right now. I know it's still an invest, but it's nowcasting time even though it's early. Also, East Caribbean isn't going to let storm develops until Jamaica area so we would have to be patient.
Member Since: August 1, 2011 Posts: 28 Comments: 7913
Can someome post 500 mb NH heights for models avgs thanks!!
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Quoting 2016. moonlightcowboy:


Good reasoning for sure. I just don't see anything much but a mostly disorganized mess. Looked much better six or eight hours ago.

M

Thank you, Sir, I've been trying to catch up with no view of 97L since 11am.
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Quoting 1973. Astrometeor:


It's a Labor Day for workers, not for educators and students. Education never stops.
That off day is added to Thanksgiving break so I can't really complain in long term... also, educators is workers and they got union too like all workers. Just saying.
Member Since: August 1, 2011 Posts: 28 Comments: 7913
Quoting 2012. Camille33:

Ukmet has always outperform it!!
That I disagree with as the GFS outperformed all the models last year. And for once can you stop yelling please.
Member Since: June 30, 2013 Posts: 11 Comments: 7698
Quoting 1994. GTstormChaserCaleb:
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.


just saying Scottsvb is one of the best on this blog..PERIOD!!!! I don't know why some are bashing the GFS...again the GFS so far with this system has been correct has it not. Tomorrow the GFS might even show something....UNTIL it shows nothing while something is there....I will stick with the GFS until proven wrong.
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Quoting 2009. daddyjames:


At the moment they are only forecasting one to develop - the southern one, but then they took that into Hispanolia as a T-wave.

Forecast the northern part to travel north of PR and wander around a bit.

Since most of the convection has waned in the southern section (the part just west of the Antilles at the moment, this appears to be the weaker section. At least in my totally amateurish evaluation. So the 2am TWDAT should be an interesting read.

OK, I gotcha, I had modified the previous quote you replied to (#1996)and mentioned that I would suspect if one was to be chosen it would be the southern one but I'm not an expert by any means as well.
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Quoting 2014. GTstormChaserCaleb:
It's true these ULL's is messing up the atmosphere for our tropical systems this year that have tried to develop closer to home. The Eastern Atlantic has contended with the stable airmass produced by the outbreaks of SAL.

I remember in one of Levi's tidbits in the beginning of the season he was saying that there were going to be a lot of ULL and he explained why. I think they were breaking off of troughs or something?
Member Since: May 12, 2012 Posts: 11 Comments: 2394
Quoting 2011. RGVtropicalWx13:
Hmm pre-98L in the nw Caribbean looks decent right now. I'm sure it has a shot. Mexico OR Not.

Looks like more rain for me that's all that may change
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2017. sar2401
Quoting redwagon:


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.

Red, 97L is is in a state of near collapse. Forget annular. If it doesn't get it's act together by sunrise, it's in big trouble.
Member Since: October 2, 2004 Posts: 0 Comments: 13464
Quoting 2003. redwagon:


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.


Good reasoning for sure. I just don't see anything much but a mostly disorganized mess. Looked much better six or eight hours ago.
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Quoting 1996. 954FtLCane:

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.


Currently, the Euro and the GFS have the southern portion getting entangled in Hispanolia and Cuba. Then continuing off to the west.
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Quoting 1975. swflurker:
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?
It's true these ULL's is messing up the atmosphere for our tropical systems this year that have tried to develop closer to home. The Eastern Atlantic has contended with the stable airmass produced by the outbreaks of SAL.
Member Since: June 30, 2013 Posts: 11 Comments: 7698
Gabrielle
Member Since: May 12, 2012 Posts: 11 Comments: 2394
Quoting 2008. sar2401:

I think several of us said it was a bad idea to change it over to the supercomputer during hurricane season. This seems to bear out that prediction. Do software and hardware upgrades at non-critical times.

Ukmet has always outperform it!!
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Hmm pre-98L in the nw Caribbean looks decent right now. I'm sure it has a shot. Mexico OR Not.
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Quoting 2007. opal92nwf:
Am I just weird or is anyone else here looking at the comment numbers thinking about the hurricane seasons that they represent? Lol

LOL, for me it was the year I was born. I'm not saying which post that was though.
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Quoting 1996. 954FtLCane:

and why not either both or neither?


At the moment they are only forecasting one to develop - the southern one, but then they took that into Hispanolia as a T-wave.

Forecast the northern part to travel north of PR and wander around a bit.

Since most of the convection has waned in the southern section (the part just west of the Antilles at the moment, this appears to be the weaker section. At least in my totally amateurish evaluation. So the 2am TWDAT should be an interesting read.
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2008. sar2401
Quoting GTstormChaserCaleb:
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.

I think several of us said it was a bad idea to change it over to the supercomputer during hurricane season. This seems to bear out that prediction. Do software and hardware upgrades at non-critical times.
Member Since: October 2, 2004 Posts: 0 Comments: 13464
Am I just weird or is anyone else here looking at the comment numbers thinking about the hurricane seasons that they represent? Lol
Member Since: May 12, 2012 Posts: 11 Comments: 2394
Quoting 1973. Astrometeor:


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


I start school on Tuesday, not Monday.
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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.
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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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