Lesser Antilles Disturbance 97L Still Disorganized

By: Dr. Jeff Masters , 2:34 PM GMT on September 03, 2013

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A tropical wave over the Lesser Antilles Islands (Invest 97L) is moving west-northwest at 10 mph, and is bringing sporadic heavy rain showers to the islands. Top sustained winds observed in the islands as of 10 am AST Tuesday were mostly below 15 mph. Heavy thunderstorm activity has been low since Monday, and is spread out, as seen on satellite loops. The thunderstorms are poorly organized, and there is no sign of a well-organized surface circulation. Martinique radar shows little evidence of rotation to the echoes, and no low-level spiral bands forming. Upper level winds are favorable for development, with wind shear a low 5 - 10 knots, and an upper-level anticyclone overhead. An area of dry air from the Saharan Air Layer (SAL) surrounds 97L and is interfering with development, though the the 12Z Tuesday balloon sounding from Guadeloupe near the center of 97L showed moist air through the entire depth of the atmosphere.


Figure 1. Latest satellite image of Invest 97L.

Forecast for 97L
Wind shear is expected to be low through Friday, and ocean temperatures will be warm, 29°C. The disturbance has not been able to generate enough thunderstorms to moisten the surrounding atmosphere much, and dry air may continue to slow down development over the next few days. The models take 97L to the west-northwest, bringing it near or over Puerto Rico or Hispaniola on Wednesday night. A track over the high mountains of Hispaniola would disrupt the circulation of 97L, forcing the storm to regroup on Thursday over the Southeast Bahamas and Turks and Caicos Islands. The best chance for development of 97L would appear to be on Friday, after the storm has finished its encounter with Hispaniola. This morning's 00Z run of the experimental GFDL ensemble--which produces 10 simulations with slightly varying initial conditions to create a plume of potential storm tracks--foresees that once 97L organizes into a tropical depression, it might take only two days for it to intensify into a hurricane to the north of Hispaniola. The wave will bring heavy rain showers to the Lesser Antilles islands on Tuesday and Wednesday, and this activity will likely spread to Puerto Rico, the Virgin Islands, the Dominican Republic, and Haiti on Wednesday and Thursday. These rains will be capable of causing life-threatening flash flooding and mudslides in mountainous regions of 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 over the Central Bahamas on Saturday. There will be a strong trough of low pressure along the U.S. East Coast this weekend, which will be capable of turning 97L to the north before the storm can hit the U.S. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC left the 5-day odds of formation of 97L at 50%, and 2-day odds at 20%. The Hurricane Hunters are on call to investigate 97L Wednesday afternoon. The flight scheduled for today will likely be cancelled. The Hurricane and Severe Storm Sentinel Mission, a 5-year field project utilizing two remotely crewed Global Hawk aircraft to overfly tropical storms and hurricanes, will have one of their aircraft investigate 97L today, and again on Wednesday. You can follow the progress of the aircraft using NASA's live-plane tracker map (Global Hawk AV6 is tail number NASA872, and Global Hawk AV1 is tail number NASA871.)

98L off the coast of Africa and a Yucatan Peninsula tropical wave
A tropical wave that emerged from the coast of Africa on Monday (Invest 98L) is expected to track northwest over the Cape Verde Islands. This course will take 98L into a region of ocean where historically, very few tropical cyclones have made the long journey across the Atlantic to affect North America. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC put the 5-day odds of development at 20%.

A tropical wave over Mexico's Yucatan Peninsula has a respectable area of heavy thunderstorms associated with it that is bringing heavy rains. This activity will push over the extreme Southern Gulf of Mexico's Bay of Campeche on Wednesday. The wave will have two days over water to develop before moving ashore on the Mexican coast between Veracruz and Tampico on Friday. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC put the 5-day odds of development at 30%, and 2-day odds at 20%.

Jeff Masters

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Quoting 756. CybrTeddy:


Not in 19 years, and that was a deep El Nino.
This could be very well our first another record I want to broke. last year only two reach MH and only for 6 hours each.
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766. TXCWC
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765. JLPR2
97L took over the ULAC, so the disturbance to the east related to the other TW is getting shredded by wind-shear.

Member Since: September 4, 2007 Posts: 7 Comments: 8747
some models shifted back west a little




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97L wants to go W for awhile.
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762. IKE

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Quoting 672. Levi32:


At least someone gets it lol.

Dry air was a problem in the midlevels till about yesterday afternoon. Why they kept it at the 8am adv...I don't know.
Member Since: January 22, 2006 Posts: 0 Comments: 1723
Convection still rising over 97L and there seems to be a developing MLC over the LLC. Honestly, it seems to me liek all it needs for TD status is more convection, and it doesn't seem to be feeling DMIN at all right now so I wouldn't be surprised if it got there overnight.
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Quoting 757. VAbeachhurricanes:


What makes you say that?


Me and a few other bloggers speculate that if this season doesn't use up enough of the energy, then it will be left over and boost next season.
Member Since: October 20, 2012 Posts: 7 Comments: 2882
Quoting 753. TomTaylor:
Actually, it looks like you were hitting the nail on the head, at least with the PDO. The -PDO may be largely responsible for the unfavorable SST profile we have seen set up in the northern Atlantic this year. If you compare this year's SST anomaly pattern so far to what we normally see in a -PDO year, the correlation is remarkable:

-PDO correlated with north Atlantic SSTs for Jul-Aug




Jul-Aug 2013 SST Anomalies




It appears the PDO is largely explaining the warm mid-latitude SST anomalies in the Atlantic. The warm mid-latitude SSTs limit rising motion on the equatorial side of the Hadley cell, killing tropical activity in our basin and across the Pacific. The same is also true in the West Pacific basin where mid-latitude SSTs are well above average and creating a similar problem for tropical cyclone activity. Furthermore, the PDO's ability to regulate the ENSO (keeping it around La Nina to neutral for the last few years) is keeping the global tropics fairly cool, further limiting tropical cyclone activity. The PDO continues to amaze me with how much influence it has on the entire global atmospheric circulation.


Well the top image isn't actually that unfavorable. A band of cooler SSTs along 30N relative to warm SSTs north and south is what is usually associated with above-average hurricane activity. The vanilla negative PDO pattern is not unfavorable for the Atlantic.

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Quoting 748. FunnelVortex:


The thing is, if this season doesn't get it's act together, next season could get pretty bad...


What makes you say that?
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Quoting 754. allancalderini:
Not all of them produce majors I believe there have been seasons without majors.


Not in 19 years, and that was a deep El Nino.
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It does have that "look" about it.

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Quoting 690. CybrTeddy:


I'm in the "hey, major hurricanes happen even in the most boring of seasons" level.
Not all of them produce majors I believe there have been seasons without majors.
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Quoting 728. CybrTeddy:


Must be.
Actually, it looks like you were hitting the nail on the head, at least with the PDO. The -PDO may be largely responsible for the unfavorable SST profile we have seen set up in the northern Atlantic this year. If you compare this year's SST anomaly pattern so far to what we normally see in a -PDO year, the correlation is remarkable:

-PDO correlated with north Atlantic SSTs for Jul-Aug




Jul-Aug 2013 SST Anomalies




It appears the PDO is largely explaining the warm mid-latitude SST anomalies in the Atlantic. The warm mid-latitude SSTs limit rising motion on the equatorial side of the Hadley cell, killing tropical activity in our basin and across the Pacific. The same is also true in the West Pacific basin where mid-latitude SSTs are well above average and creating a similar problem for tropical cyclone activity. Furthermore, the PDO's ability to regulate the ENSO (keeping it around La Nina to neutral for the last few years) is keeping the global tropics fairly cool, further limiting tropical cyclone activity. The PDO continues to amaze me with how much influence it has on the entire global atmospheric circulation.
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Quoting 636. opal92nwf:
What's this, what's this?!! I see?
It reminds me of Erin models bring her south and this one looks poise to do the same.
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Uh Oh........Global Warming........Guess Politics are next....Out for a break...Season 7 of 24 here I come. Aloha
Member Since: September 18, 2010 Posts: 0 Comments: 5243
Off Invest,
Member Since: July 3, 2005 Posts: 427 Comments: 129439
Quoting 742. nash36:


LOL!! I think that pretty much sums up the season thus far....

A farto.


The thing is, if this season doesn't get it's act together, next season could get pretty bad...
Member Since: October 20, 2012 Posts: 7 Comments: 2882
Quoting 733. GTstormChaserCaleb:
Explain the strong ridging in the far eastern atlantic and fall like troughs, and that may be your answer, Upper Level Lows splitting off those troughs causing shear. So what's the main thing causing all this? Global Warming? I mean I really do think it is time to start taking Global Warming into consideration for the lack of activity so far this year and the recurving pattern the last few seasons.


Wait like 20 more years
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Who, what, why: How does a skyscraper melt a car?

Excerpt:

The car wasn't the only casualty. There have also been reports of a smouldering bicycle seat, singed fabric and blistered paintwork.
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Quoting 738. wpb:
peak of season and 97l is the topic. a bust so farto say the least last week of sept first two of oct could be heavy.otherwise all the pro predictors will eat crow.
well if its crow it will be for us all most were seeing a big season
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Fish storms? How about a reptile storm in Mississippi? Record for biggest gator taken in Mississippi broken twice in one day.


Mississippi's fattest alligator tale
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Quoting 658. Camille33:
There is a growing risk of a significant tropical cyclone impacting the se conus by mid part of next week.
Please Show Us.
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Quoting 739. moonlightcowboy:


I agree. 97L has been a farto. ;P


LOL!! I think that pretty much sums up the season thus far....

A farto.
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Quoting 738. wpb:
peak of season and 97l is the topic. a bust so farto say the least last week of sept first two of oct could be heavy.otherwise all the pro predictors will eat crow.

ggo bicker somewhere else
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Quoting 738. wpb:
peak of season and 97l is the topic. a bust so farto say the least last week of sept first two of oct could be heavy.otherwise all the pro predictors will eat crow.


I agree. 97L has been a farto. ;P
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738. wpb
peak of season and 97l is the topic. a bust so farto say the least last week of sept first two of oct could be heavy.otherwise all the pro predictors will eat crow.
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Quoting 688. Levi32:


I haven't seen any evidence that the actual circulation of 97L has been invaded by dry air. The outflow boundaries to the northwest I think are being caused by the accelerating trade wind flow to their west, which is pulling air down, causing convective cells to collapse. Such downdrafts can then in turn create some dry air along the northern periphery, but the point is I don't think dry air has ever really been an issue for 97L. It's been nearby, but not entrained. The inhibitor has been elongated structure and lack of the convergence necessary to sustain a CDO.


Totally agree! The broad, elongated structure has been unconventional, and it's been very difficult for it to overcome. But I do think dry air has been a contributor to hindering development. Another blogger, Beell I think, suggested there may be/have been more dry air at the surface than water vapor charts have revealed. That, coupled with "some" SA continental dry air certainly has not helped development.
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735. MahFL
Quoting 718. Tazmanian:



you cant call it OTS after it all ready it land


You can really as no tropical cyclone has yet formed from 97L.
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Quoting 724. TomTaylor:
OR there could be something else going on that you are missing lol

And yes, I agree about the heat being focused in midlatitudes. But that is not necessarily a result of the PDO and AMO state. AMO and PDO both tend to focus the warmest SSTs around 10-20N in the tropical Atlantic, based off correlations.
Explain the strong ridging in the far eastern atlantic and fall like troughs, and that may be your answer, Upper Level Lows splitting off those troughs causing shear. So what's the main thing causing all this? Global Warming? I mean I really do think it is time to start taking Global Warming into consideration for the lack of activity so far this year and the recurving pattern the last few seasons.
Member Since: June 30, 2013 Posts: 12 Comments: 8774
Surface map. East coast currently has blocking High pressure building in.
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Quoting 729. BrandenCordeiro:
97L is looking very good in my opinion.


Mine too.
Member Since: October 20, 2012 Posts: 7 Comments: 2882
Quoting 683. Ameister12:
It ain't over 'til the fat lady sings. (Or 'til it's November 30th)




Sorry, couldn't resist. Although I cannot see her big shadow yet in this season, lol.

Good night with this, stay well with 97L (rhyming!).
Member Since: October 25, 2008 Posts: 62 Comments: 6524
97L is looking very good in my opinion.
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Quoting 724. TomTaylor:
OR there could be something else going on that you are missing lol

And yes, I agree about the heat being focused in midlatitudes. But that is not necessarily a result of the PDO and AMO state. AMO and PDO both tend to focus the warmest SSTs around 10-20N in the tropical Atlantic, based off correlations.


Must be.
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Member Since: July 3, 2005 Posts: 427 Comments: 129439
Quoting 719. nrtiwlnvragn:


Once a month WPC does a TWO to demonstrate their capability as NHC's backup.


Gotcha, makes sense. I thought the writing was a bit off per usual, didn't realize it was a different agency.
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Some cold tops in there
Member Since: September 18, 2010 Posts: 0 Comments: 5243
Quoting 717. CybrTeddy:


Clearly not, seeing as 2013 is the current state it's in. What I'm trying to say is that there's no focus of heat in our basin due to warm water in the northern latitudes of the Atlantic and near the poles.
OR there could be something else going on that you are missing lol

And yes, I agree about the heat being focused in midlatitudes. But that is not necessarily a result of the PDO and AMO state. AMO and PDO both tend to focus the warmest SSTs in the tropical Atlantic, based off correlations. That has not been the case this year.
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Make the trough or miss the trough?
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Quoting 718. Tazmanian:



you cant call it OTS after it all ready it land
It hasn't developed yet though, so if it goes over PR without developing it could go OTS.
Member Since: June 30, 2013 Posts: 12 Comments: 8774
Quoting 715. VAbeachhurricanes:
Is there a reason the TWO was written by the Weather Prediction Center in Maryland and not by the NHC?
they have been doing those a few times this season its like the third one I seen this season

maybe give some interns a chance to write up stuff or a test for when Miami goes off line in a storm or other event
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Quoting 715. VAbeachhurricanes:
Is there a reason the TWO was written by the Weather Prediction Center in Maryland and not by the NHC?


Once a month WPC does a TWO to demonstrate their capability as NHC's backup.
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Quoting 716. GTstormChaserCaleb:
Watch it go OTS. :D



you cant call it OTS after it all ready it land
Member Since: May 21, 2006 Posts: 5091 Comments: 115437
Quoting 712. TomTaylor:
?

-PDO AMO and neutral to weak La Nina conditions are arguably the most favorable conditions you could ask for in the Atlantic. Multi-year La Ninas can become a problem, but we haven't been in a full blown multi-year La Nina. -PDO and neutral to near Nina conditions may help partially explain the global downturn in activity, but not the Atlantic's.


Clearly not always, seeing as 2013 is the current state it's in. What I'm trying to say is that there's no focus of heat in our basin due to warm water in the northern latitudes of the Atlantic and near the poles. Also, I'm aware we haven't been in a true La Nina state since 2010, I don't believe we've recorded a multi-year neutral phase which is interesting, I'm just comparing that the effects might be similar to what we saw in the 70s.
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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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