Dangerous Caribbean disturbance 95L close to tropical storm strength

By: Dr. Jeff Masters , 13:57 GMT le 23 septembre 2010

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A tropical wave (Invest 95L), moving westward at 15 mph though the south-central Caribbean, will bring gusty winds and heavy rain squalls to the northern coasts of Colombia and Venezuela this morning, as well as the Netherlands Antilles Islands. This disturbance will bring dangerous flooding rains to the countries bordering the Western Caribbean this weekend, and may also be a threat to the U.S. Gulf of Mexico coast late next week. A hurricane hunter aircraft is in 95L, and found a large region of surface winds of 35 - 45 mph to the east of 95L's center. If they find a closed circulation, 95L will be upgraded to Tropical Storm Matthew today. Satellite loops show that heavy thunderstorm activity has increased markedly in recent hours, with a solid curved band of intense thunderstorms growing to the northeast of 95L's center. Low-level spiral bands are also developing to the southeast of the center, but a closed surface circulation is not yet obvious from satellite imagery.


Figure 1. Morning satellite image of 95L.

Forecast for 95L
An upper-level high pressure system lies to the west of 95L, near the coast of Nicaragua. The clockwise flow of air around this high will bring a moderate 10 - 15 knots of wind shear over 95L today. By Friday, 95L will move more underneath this upper-level high, causing the shear to decline. The SHIPS model forecasts that shear will fall to the low range, 5 - 10 knots, by Friday afternoon. This drop in shear may allow for rapid intensification of 95L as it approaches landfall near the Nicaragua/Honduras border on Friday night and early Saturday morning. NHC is giving the disturbance an 80% chance of developing into a tropical depression by Saturday.


Figure 2. Forecast track of 95L from an ensemble of runs of the GFS model done at 2am EDT this morning.

The future of 95L depends critically upon the storm's interaction with land over the coming days. If 95L misses making landfall in Nicaragua and Honduras, and instead skirts the north coast of Honduras, the storm is likely to intensify into a hurricane by Monday, as predicted by last night's 00Z (8pm EDT) run of the GFDL model. However, if 95L spends significant time over Honduras, as predicted by the latest 06Z (2am EDT) run of the GFDL model, the storm will likely stay below hurricane strength. 95L is being forced just north of due west by a strong ridge of high pressure. This ridge will keep the storm moving at 15 mph through Saturday. On Sunday, a trough of low pressure diving southwards over the Eastern U.S. will weaken the steering currents over the Western Caribbean and cause 95L to slow and turn more to the north. 95L will begin a period of slow and erratic movement on Sunday that may last many days, as the storm wanders in the Western Caribbean and over Belize, Honduras, and Mexico's Yucatan Peninsula. If the center of 95L spends significant time over water, the storm could easily develop into powerful and dangerous Hurricane Matthew. If the center remains mostly over land, 95L will still generate extremely heavy rains over Central America, but remain below hurricane strength. By late next week, the trough of low pressure over the Eastern U.S. may lift out, allowing a ridge of high pressure to build in and force 95L westwards across the Yucatan Peninsula and into the Gulf of Mexico's Bay of Campeche. Alternatively, the trough of low pressure over the Eastern U.S. may amplify, drawing 95L northwards across Western Cuba and into Florida. The uncertainties in the long-range fate of 95L are high, and depend strongly on slight variations in its track that determine how much time the storm spends over land. One measure of the uncertainty in 95L's future track can be gained by viewing the ensemble forecast from the GFS model. An ensemble forecast is generated by taking the initial conditions in the atmosphere and making slight variations in the temperature, pressure, and humidity fields. Twenty or so tweaks of the initial conditions are made, and the GFS model run twenty separate times for each new set of initial conditions. The resulting ensemble of model runs gives one an idea of how sensitive the future track of the storm might be to errors in characterizing the initial state of the atmosphere. As one can see from this morning's GFS ensemble run (Figure 2), there are a wide range of possibilities for where 95L might go. The main thing I am confident of at this point is that 95L will generate very heavy rains over Nicaragua, Honduras, Belize, and Mexico's Yucatan Peninsula Friday through Tuesday that will likely cause dangerous flooding rains and life-threatening mudslides.

Tropical Depression Lisa
Tropical Depression Lisa continues to churn the waters of the far Eastern Atlantic. By Saturday night, upper level winds out of the west are expected to increase, bringing high wind shear of 20 - 45 knots over Lisa. The high shear may be capable of destroying the storm by early next week. It appears unlikely that Lisa will affect any land areas.

Elsewhere in the tropics
The remnants of Hurricane Julia are still spinning over the far Eastern Atlantic, and are generating some sporadic heavy thunderstorm to the north of the center of circulation. Julia's remains are being given a 10% chance of re-developing by NHC. There are no other threat areas to discuss, and none of the models is calling for development (except for 95L) over the next seven days.

Hurricane Karl's moisture causing flooding in Minnesota, Wisconsin
A plume of very moist air associated with what was Hurricane Karl last week has surged northwards over the Central U.S. over the past two days. This moisture is now being lifted over a warm front draped over Minnesota and Wisconsin, and has generated flooding rains in excess of six inches in southern Minnesota this morning. Flood warnings and flood watches are posted for a wide swath of the upper Midwest today, including most of Minnesota, northern Wisconsin, and Michigan's Upper Peninsula. The latest forecast discussion from the NWS office in Minneapolis notes that the forecast amount of moisture in the air this afternoon is similar in magnitude to the all-time record for this time of year (set on September 2, 1953.) These kinds of rain events are called Predecessor Rain Events (PREs), because they typically precede the actual arrival of the rain shield of a tropical storm.


Figure 3. Radar estimated rainfall over Minnesota.

Next post
I'll have an update on 95L later today. The timing will depend upon what the Hurricane Hunters find.

Jeff Masters

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672. HCW
Quoting WxLogic:


I truly believe NHC doesn't want to get started drawing 5 days cone quite yet... they'll wait until 5PM for that one it seems.


They cone has already been finished and we will see it in the next 10 minutes
Member Since: Posts: Comments:
Quoting WxLogic:


I truly believe NHC doesn't want to get started drawing 5 days cone quite yet... they'll wait until 5PM for that one it seems.


I don't think so, 2PM should be a complete advisory package. The cone is simple to construct anyways, just the specified radii from the forecast points.
Member Since: 23 septembre 2005 Posts: 14 Comments: 11156
Quoting SuperYooper:


Wouldn't that be like a brother from another mother?


haha, yeah
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Quoting beell:
Ya'll still calling this a cut-off ULL?
At 700mb?

12Z GFS @ 84 hrs.


It's a cutoff low still. Just not a upper level cutoff low :-)

It's still separated from the jet stream...
Member Since: 15 juin 2010 Posts: 0 Comments: 291
HH still finding TS winds
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Quoting InTheCone:


Can't wait to see the 5 day cone!


I truly believe NHC doesn't want to get started drawing 5 days cone quite yet... they'll wait until 5PM for that one it seems.
Member Since: 14 août 2008 Posts: 4 Comments: 4972
They are going to declare it at 2:00.
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Quoting MNhockeymama:
It is weird to be in Minnesota and be affected by a Hurricane - my husband is in southern MN and has experienced some of the flooding. The rain hasn't stopped here (near Mpls) since late yesterday afternoon; sometimes coming down in sheets.



Yes it is, just got an email from daughter and the city of Arcadia,WI is under state of emergency due to flooding. S/SE MN and W/C WI are getting hammered. The remnants of Karl are coming on top of the 30" rains that S. WI received from June through Aug! Very similar to what we had in the fall of 2007. corected year
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659. beell
Ya'll still calling this a cut-off ULL?
At 700mb?

12Z GFS @ 84 hrs.
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Quoting reedzone:
I can't get over how much TD15 looks like TD1, just a bit smaller.


Me neither. It's quite fascinating!
Member Since: 11 août 2010 Posts: 0 Comments: 74
should be interesting to see the track by the NHC because after this thing nears the yucatan peninsula i dont think any model has a hold on it
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Quoting StormChaser81:


1. DATA FROM AN AIR FORCE RECONNAISSANCE PLANE INVESTIGATING THE AREA
OF LOW PRESSURE IN THE SOUTHWESTERN CARIBBEAN SEA INDICATE THAT A
TROPICAL DEPRESSION HAS FORMED. THE NATIONAL HURRICANE CENTER WILL
ISSUE A SPECIAL ADVISORY AT 2 PM EDT TODAY. THERE IS A HIGH
CHANCE...100 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS.



Can't wait to see the 5 day cone!
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Might end up being a TWO at 2pm saying 'We'll initiate advisories' and then do it half hour later.

Guess we'll in a few minutes.

Btw, with this 2nd low, the NAM also shows increased energy and convection around the west coast of Costa Rica by 72 to 84 hours. While the multiple vortices theory could end up being correct, I do think keeping an eye on the neighbour basin might be worth it. Just to see if that small hint has any credibility or not.
Member Since: 23 août 2008 Posts: 7 Comments: 5300
Quoting reedzone:
I can't get over how much TD15 looks like TD1, just a bit smaller.


looks a lot more "circular" than TD 1
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Quoting StormChaser81:


1. DATA FROM AN AIR FORCE RECONNAISSANCE PLANE INVESTIGATING THE AREA
OF LOW PRESSURE IN THE SOUTHWESTERN CARIBBEAN SEA INDICATE THAT A
TROPICAL DEPRESSION HAS FORMED. THE NATIONAL HURRICANE CENTER WILL
ISSUE A SPECIAL ADVISORY AT 2 PM EDT TODAY. THERE IS A HIGH
CHANCE...100 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS.



beat me to it
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I can't get over how much TD15 looks like TD1, just a bit smaller.
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chances upped to 100%

http://www.nhc.noaa.gov/gtwo_atl.shtml

lawlz
Member Since: Posts: Comments:


1. DATA FROM AN AIR FORCE RECONNAISSANCE PLANE INVESTIGATING THE AREA
OF LOW PRESSURE IN THE SOUTHWESTERN CARIBBEAN SEA INDICATE THAT A
TROPICAL DEPRESSION HAS FORMED. THE NATIONAL HURRICANE CENTER WILL
ISSUE A SPECIAL ADVISORY AT 2 PM EDT TODAY. THERE IS A HIGH
CHANCE...100 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS.

Member Since: Posts: Comments:
Quoting CosmicEvents:
That does seem to be the word of the season. One of the words for this season:)

I'm understanding "monsoonal" really well right now - holy cats its comin' down right now. I fully expect my backyard to be flooded soon.
Member Since: 4 septembre 2010 Posts: 0 Comments: 124
This map indicates drier areas east of centra Texas. Climatology seems on track to bring tropical moisture to areas around Baton Rouge and eastward. The form may that of Matthew.

Member Since: 30 septembre 2005 Posts: 0 Comments: 1606
Quoting Hurricanes101:


I still see them at 900 feet


yea going in for another run
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Quoting moonlightcowboy:
I see the theme is still "monsoonal." ;P

Ok.
That does seem to be the word of the season. One of the words for this season:)
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Quoting InTheCone:
12z CMC


Hmm...
Member Since: 14 août 2008 Posts: 4 Comments: 4972
hey look

TD15, lol.

I just checked the FTP site before I posted too, sneaky buggers.
Member Since: 30 janvier 2010 Posts: 0 Comments: 3259
thanks everyone. back to work
Member Since: 24 août 2006 Posts: 0 Comments: 1867
Quoting SuperYooper:


I don't put anything past the UP. It will probably snow. Glad I change the oil on the blower.

OMG - God forbid! That would be wretched.
Member Since: 4 septembre 2010 Posts: 0 Comments: 124
Quoting Hurricanes101:


I still see them at 900 feet


LOL. My bad. They tricked me by going up to 1000.
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Quoting Levi32:


The track is again impossible to nail down right now as the models always have a hard time dealing with cut-off upper lows, and since the main steering influence on Matthew is likely to be a cut-off upper low, we are going to see a lot of different things show up on the models.

Yes an upper trough digging down may cause some wind shear and dry air which would be moderating factors in the Gulf of Mexico.

I think no matter what the trough does something is going to get drawn north out of the Caribbean next week, somehow. We'll see how it goes. Given the monsoonal nature of Matthew's development it wouldn't be a stretch to imagine new low centers forming while he is dealing with central America, but we'll see.


Ah, so "2 from 1" to put it simply, is possible.
Member Since: 24 août 2006 Posts: 0 Comments: 1867
Quoting weatherman12345:
my question is why they named it td15 when they are found 45 mph sustained winds


NHC discussion will answer that momentarily, no need to speculate anymore.
Member Since: 30 janvier 2010 Posts: 0 Comments: 3259
T.C.F.W.
015L/TD/XX
MARK
13.48N/75.56W


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Quoting Seastep:
And there you go... they're leaving.

Kind of surprised, actually. They usually stay in there longer.


I still see them at 900 feet
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12z CMC
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Quoting weatherman12345:
my question is why they named it td15 when they are found 45 mph sustained winds


Not a very well defined center.
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Quoting BobinTampa:


is that the big lake they call Gitche Gumme?


Yeah, but nobody says "I'm going to get my dose of shrinkage swimming in Gitche Gumme." To anyone here, Gitche Gumme is a campground off of M28 about 3 miles from my house.
Member Since: 18 août 2010 Posts: 14 Comments: 1602
I see the theme is still "monsoonal." ;P

Ok.
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And there you go... they're leaving.

Kind of surprised, actually. They usually stay in there longer.
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Quoting reedzone:
I fully believe we have a Tropical Depression in the Caribbean. Advisories should be out by 5 p.m. if not sooner.


we now have TD 15

LOL you posted right after the update
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Quoting Cotillion:
Bets on TD15 or TS Matthew?

(As in which will it be...)


Based on the current setup... I will go with TD15 by 2PM TWO and Matthew by 5PM.
Member Since: 14 août 2008 Posts: 4 Comments: 4972
Quoting txag91met:
This thing is already close to being TS Matt...what is taking NHC so long to upgrade it?



There is a plane in there right now formulating an accurate discussion /track from the NHC. As soon as the plane completes you'll have your storm.
Member Since: 30 janvier 2010 Posts: 0 Comments: 3259

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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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