93L slow to develop, but bringing heavy rains to Haiti

By: Dr. Jeff Masters , 1:50 PM GMT on June 22, 2010

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A modest region of intense thunderstorms (Invest 93L) is over the central Caribbean, a few hundred miles south of Hispaniola. This disturbance has the best chance to become Tropical Storm Alex of any system we've seen so far this year. We don't have any buoys near 93L, but pressures at the ground stations surrounding the storm are not falling. A pass of the ASCAT satellite over the Central Caribbean at 9:45 pm EDT last night revealed a modest wind shift associated with 93L, but nothing at all close to a surface circulation. Top surface winds seen by ASCAT were 15 - 20 mph. Water vapor satellite loops show that 93L is embedded in a large region of moist air. The atmosphere over the Caribbean has moistened over the past day, which should aid development of 93L. Wind shear is a low 5 - 10 knots. The high wind shear associated with the strong winds of the subtropical jet stream are over the northern Caribbean, too far north to interfere with development, but close enough to provide good upper-level outflow for the storm. Visible satellite loops show high level cirrus clouds streaming away from 93L to the northeast, evidence of the upper-level outflow channel that is developing to the storm's north. Sea Surface Temperatures are plenty warm, a record 29 - 30°C. The Madden-Julian oscillation (MJO) currently favors upward motion over the Caribbean, which will act to increase the chances of tropical storm formation this week. The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased. The main negative for 93L continues to be lack of spin. The University of Wisconsin 850 mb relative vorticity analysis is showing that spin at 850 mb (roughly 5,000 feet in altitude) has increased over the past day, but 93L needs to acquire additional spin before it can grow more organized. I speculate that it is this lack of spin that contributed to the loss of much of 93L's heavy thunderstorm activity last night. The storm is now going through a cycle where it is building another respectable mass of heavy thunderstorms, and the increased inflow of low-level air that will feed these thunderstorms will likely enhance 93L's spin today. The Hurricane Hunters are on call to investigate 93L on Wednesday afternoon.


Figure 1. Morning visible satellite image of the central Caribbean disturbance 93L.

Forecast for 93L
NHC is giving 93L a 40% chance of developing into a tropical depression by Thursday morning, which is a reasonable forecast. Given the storm's current lack of spin and relatively modest amount of heavy thunderstorms, the earliest I'd expect 93L to become a tropical depression would be Wednesday afternoon, with Thursday more likely. Wind shear is expected to be low, less than 10 knots, over the central and western Caribbean this week. Water temperatures will be warm, dry air absent, and the MJO favorable. I don't see any major impediments to the storm becoming a tropical depression by Thursday, and it is a bit of a surprise to me that the computer models have been reluctant to develop 93L. The GFS, NOGAPS, and UKMET models do not develop 93L, and the ECMWF model doesn't develop 93L until after it crosses the Yucatan Peninsula and enters the Gulf of Mexico in a about a week. The current (2am EDT) run of the GFDL model predicts 93L will be a weak tropical storm in the Gulf of Mexico in five days; its previous run had 93L as a major hurricane in the Gulf. Given all this model reluctance and the current disorganization of 93L, I give the storm a low (less than 20% chance) of becoming a hurricane in the Caribbean. Expect 93L to bring flooding rains of 3 - 6 inches to Jamaica, eastern Cuba, and southwestern Haiti today through Wednesday. These rains will spread to the Cayman Islands and central Cuba by Thursday, and western Cuba and Mexico's Yucatan Peninsula on Friday. The current run of the SHIPS model has 93L slowing down late this week to a forward speed of just 6 knots (7 mph) from its current speed of about 10 mph, in response to a weakening in the steering currents. A trough of low pressure is expected to swing down over the Eastern U.S. early next week. If this trough is strong enough and 93L develops significantly, the storm could get pulled northwards and make landfall along the northern Gulf of Mexico coast in the oil spill region. This is the solution of the Canadian GEM model. If 93L stays weak and/or the trough is not so strong, the storm would get pushed west-northwestwards towards the Texas coast. This is the solution of the ECMWF model. The amount of wind shear in the Gulf of Mexico next week is highly uncertain. There is currently a band of high shear near 30 knots over the Gulf, and some of the models predict this shear will remain over the Gulf over the next 7 - 10 days. However, other models predict that this band of high shear will retreat northwards and leave the Gulf nearly shear-free. The long-term fate of 93L remains very murky. My main concerns at this point are the potential for 3 - 6 inches of rain in Haiti over the next two days, and the possibility 93L could become a hurricane in the Gulf of Mexico next week.

Elsewhere in the tropics
None of the reliable computer models is calling for tropical cyclone formation elsewhere in the Atlantic over the next seven days.

Floods in China and Burma kill over 250
The deadliest and most destructive weather-related disaster on the planet so far this year is occurring in southern China and northern Burma, where a week of heavy rains has caused flooding that has claimed over 250 lives. The heavy rains and floods ravaging 10 southern Chinese provinces had killed 199 and left 123 missing as of 11:00 a.m. Tuesday, a Ministry of Civil Affairs statement said. Damage is estimated at $6.2 billion. Floods and landslides in neighboring areas of Myanmar (Burma) have claimed at least 63 lives in the past week.


Figure 2. Paramilitary policemen help evacuate residents from Wanjia village of Fuzhou City, East China's Jiangxi province, June 22, 2010. Days of heavy rain burst the Changkai Dike of Fu River on June 21, threatening the lives of 145,000 local people. Local authorities have ordered immediate evacuation, and the army and paramilitary police have begun conducting rescue operations. Image credit: Xinhua.

Wind and ocean current forecast for the BP oil disaster
Southeast to east winds less than 10 knots will blow in the northern Gulf of Mexico today through Saturday, according to the latest marine forecast from NOAA. The resulting weak ocean currents should cause little motion of the oil slick, according to the latest trajectory forecasts from NOAA and the State of Louisiana. The long range outlook is uncertain, and will depend upon what 93L does.

Resources for the BP oil disaster
My post, What a hurricane would do the Deepwater Horizon oil spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA's interactive mapping tool allows one to overlay wind and ocean current forecasts, oil locations, etc.
Gulf Oil Blog from the UGA Department of Marine Sciences
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Synthetic Aperture Radar (SAR) imagery from the University of Miami

"Hurricane Haven" airing again this afternoon
Tune into another airing of my live Internet radio show, "Hurricane Haven", at 4pm EDT today. Listeners will be able to call in and ask questions. The call in number is 415-983-2634, or you can post a question in the comments area on my blog. You can also email the questions to me today before the show: jmasters@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line. Some topics I'll cover today on the show:

1) The latest on 93L
2) Which model is the most reliable?

Today's show will be 30 - 40 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

Jeff Masters

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the blog pick up
Member Since: May 21, 2006 Posts: 5091 Comments: 115072
Quoting Stormchaser2007:
2100 UTC 850 Vort

That would support the broad area of low pressure SE of Jamaica.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
1644. IKE
Quoting MiamiHurricanes09:
Huh?


You asked what if the trough is slower or weaker. I said that would change the outcome of where 93L goes.
Member Since: June 9, 2005 Posts: 23 Comments: 37858

Quoting Stormchaser2007:
2100 UTC 850 Vort



that would support the west wind too
Member Since: March 10, 2010 Posts: 1 Comments: 7677
Not liking the latest CMC. I know it is the CMC but holy cow that is one heck of a low in the central Gulf. That is bad news if that verifies haha.
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1641. xcool
2010-Jun-22 20:00 N 17°30' W 075°24' 21 21.3 090 28k 1011.0 5.4 1.0 26.6 23.0
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2100 UTC 850 Vort

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Can someone post the link for the 18z gfs...TIA
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1637. centex
Quoting Acemmett90:

lol why did u write it like that then
Crazy, last time I was in Jamaica they where proud of how they talked. It’s no shame or prejudice. It’s just a way to appreciate them to acknowledge we like it to. The world is not all the same, and I love that.
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Quoting IKE:


Different outcome.
Huh?
Member Since: September 2, 2009 Posts: 130 Comments: 21193
Hey Pottery, you on? Dudus in custody. Not sure if he was caught or he turned himself in. Story still developing.
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1632. Dakster
Trivia Question:

What were the last years that a Major Hurricane formed in the GOM during June/July?
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Quoting Tazmanian:
i hop where not starting too see Rapid intensification with 93L
Dude, lol.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
1630. IKE
Quoting MiamiHurricanes09:
What if the trough stalls or speeds up. Don't say "NOT", specially with weather.


Different outcome.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
18z SHIPS shear looks interesting...

TIME (HR) 0 6 12 18 24 36 48 60 72 84 96 108 120
V (KT) NO LAND 25 26 28 31 35 42 52 64 71 79 86 93 96
V (KT) LAND 25 26 28 31 35 42 52 64 71 79 86 55 36
V (KT) LGE mod 25 26 27 29 31 36 44 55 71 91 106 67 39

SHEAR (KT) 1 7 5 8 6 8 5 2 7 5 9 5 8
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1627. RJT185
...I still don't see it.
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Quoting Jeff9641:
Any storm that forms and moves into the gulf will NOT hit TX. Main threat is New Orleans to Tampa. Huge trough early next week in the east.
What if the trough stalls or speeds up. Don't say "NOT", specially with weather.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
1624. IKE
Quoting Hurricanes101:


but the key thing there is

18Z GFS actually keeps 93L, which it hasnt ever really done before


True...
Member Since: June 9, 2005 Posts: 23 Comments: 37858
i hop where not starting too see Rapid intensification with 93L
Member Since: May 21, 2006 Posts: 5091 Comments: 115072
Quoting StormSurgeon:
Is there anything out there to be concerned about? I dooubt it........Lots of rain on Dauphin Island, AL....no oil though.


????
Member Since: March 10, 2010 Posts: 1 Comments: 7677
Air pressure where I am is 1010mb according to my weather station.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
1620. IKE
Quoting Jeff9641:
Any storm that forms and moves into the gulf will NOT hit TX. Main threat is New Orleans to Tampa. Huge trough early next week in the east.


You may be correct about avoiding Texas.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Ike, I would be in the "forbidden zone" RFQ. A storm like that in the GOMEX almost always sparks tornadoes here in East-Central Florida.
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Quoting Tazmanian:



i think thatsa few hrs old


its not... you just always say that...
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Quoting IKE:


Track is central/eastern GOM with the GFS.


but the key thing there is

18Z GFS actually keeps 93L, which it hasnt ever really done before
Member Since: March 10, 2010 Posts: 1 Comments: 7677
Is there anything out there to be concerned about? I dooubt it........Lots of rain on Dauphin Island, AL....no oil though.
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1614. IKE
Strong trough on the 18Z GFS.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting Drakoen:


Yea. And we have one ship report of some surface westerlies so something is going on down there SE of Jamaica.
Agreed.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
1612. unf97
Quoting IKE:
New version of the GFS at 144 hours....



Yeah, this run of the GFS is jumping on board tracking whatever becomes of 93L right into the Central GOM.
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1610. xcool
42057 B 2150 16.83 -81.50 264 310 40 9.7 9.7 2.3 7 4.8 - 29.85 -0.03 84.9 85.8 77.7 - - - - - - - - - ---- ----- 1.97 6.7 - 0.98 4.2 - N/A
LCIY2 O 2100 19.70 -80.06 362 341 60 13.0 15.9 - - - - 29.88 -0.04 84.9 86.4 74.1 - - - - - - - - - ---- ----- - - - - - - -
SHIP S 2100 19.30 -81.70 383 327 60 13.0 - 3.3 1.0 - - 29.80 +0.03 85.6 87.8 73.4 5 4
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1609. IKE
Quoting ecflweatherfan:
Not liking that GFS, Ike... would pose a tornado threat on my side of the state, based on that depiction.


Track is central/eastern GOM with the GFS.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1608. IKE
GFS...both versions...take 93L over the Yucatan and then turn it toward a general northward direction. Doesn't head it toward Texas.

I bet the 18Z GFDL is similar.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1605. Drakoen
Quoting MississippiWx:
Drak-

I think if people focused more on the low clouds on that visible floater you posted, they could understand more clearly where a surface reflection is located. There is a noticeable counter-clockwise motion to the low clouds.


Yea. And we have one ship report of some surface westerlies so something is going on down there SE of Jamaica.
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Quoting Stormchaser2007:



i think thatsa few hrs old
Member Since: May 21, 2006 Posts: 5091 Comments: 115072
Not liking that GFS, Ike... would pose a tornado threat on my side of the state, based on that depiction.
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Quoting ecflweatherfan:
I am thinking still "Yellow" at 8pm... but up the chance to 30%.
Either it stays the same or slightly increases.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
1600. xcool
SHIP S 2200 10.40 -75.50 261 146 VRB 1.9 - - - - - 29.83 -0.07 81.5 - 74.1 11 6 - - - - - - - ---- ----- - - - - - - -
SHIP S 2200 19.40 -81.90 394 326 60 13.0 - 3.3 1.0 - - 29.80 +0.03 85.6 87.8 73.4 5 4 - - - - - - - ---- ----- - - - - - - -
2 observations reported for 2200 GMT
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Drak-

I think if people focused more on the low clouds on that visible floater you posted, they could understand more clearly where a surface reflection is located. There is a noticeable counter-clockwise motion to the low clouds.
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Quoting Stormchaser2007:


Indeed.


Theres also quite a few cumulonimbus atop the developing low.

Very nice.
Member Since: September 2, 2009 Posts: 130 Comments: 21193
Quoting Baltimorebirds:
In any giving season a major in the gulf will not be good.But mother nature is trying to find a way to cool off those ocean temps and what it we won't like....
The Oil!!
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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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