Caribbean disurbance 96L nearly a depression; hottest day ever in Los Angeles

By: Dr. Jeff Masters , 1:54 PM GMT on September 28, 2010

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Pressures continue to fall over the Western Caribbean this morning as a strong tropical disturbance (96L) organizes. Surface observations suggest that 96L has a large circulation covering most of the Western Caribbean, as evidenced by winds out of the southwest sustained at 29 - 34 mph observed at Buoy 42057 to the southeast of 96L's center this morning. Rotation of 96L can be seen on radar loops out of Pico San Juan, Cuba, and well as satellite imagery. The heavy thunderstorms are currently quite disorganized, but are bringing torrential rains to the Cayman Islands, Jamaica, Cuba, and Honduras. A Personal Weather Station in George Town on Grand Cayman Island has picked up 3.64" of rain in the twelve hours ending at 8am this morning. 96L is not the typical sort of disturbance one sees in the Atlantic, since it is much larger than normal. What has happened is that the atmospheric flow pattern of the Eastern Pacific has shifted eastwards into the Western Caribbean, bringing in the Eastern Pacific ITCZ (Intertropical Convergence Zone, a region of converging surface winds that creates a band of strong thunderstorms). 96L resembles the "monsoon depressions" common in India's Bay of Bengal or the Western Pacific. A monsoon depression is similar to a regular tropical depression in the winds that it generates--about 30 - 35 mph near the outer edges (and usually stronger on the eastern side of the circulation.) Monsoon depressions have large, calm centers, and can evolve into a regular tropical storms, if given enough time over water to develop a tight, closed circulation. The Hurricane Hunters are scheduled to fly into 96L this afternoon near 2pm EDT to see if it has become a tropical depression.


Figure 1. Morning radar image of 96L. Image credit: Cuban Institute of Meteorology.

Forecast for 96L
Because 96L is so large and lacks a well-defined surface circulation, it will take more time than a typical disturbance for it to spin up into a strong tropical storm. Given that the steering currents are expected to pull 96L north-northeastwards over Cuba and into South Florida and the western Bahamas on Wednesday, the storm lacks sufficient time over water to be any stronger than a 55 mph tropical storm for Florida. I think the top winds in Southeast Florida are likely to be in the 30 - 45 mph range on Wednesday. By the time 96L makes landfall in North Carolina or South Carolina on Thursday morning or afternoon, it could be as strong as a 55 - 65 mph tropical storm, but I think it is only 20% likely that 96L will make it to hurricane strength on Thursday. The primary danger from the storm is heavy rainfall. A potent upper-level low and stationary front over the U.S. East Coast have been bringing moist, tropical air from the Caribbean northwards over the past few days, bringing heavy rains that have saturated the soils. Wilmington, NC received 10.33 inches of rain yesterday, its second greatest one-day rainfall since record keeping began in 1871. Only the 13.38" that fell during Hurricane Floyd on September 15, 1999 beat yesterday's rainfall total. With 96L expected to bring another 6 - 8 inches of rain to the region later this week, serious flooding is likely, and flash flood watches are posted for the North Carolina/ South Carolina border region. South Florida is also under a flood watch, for 3 - 5 inches of rain. Flooding rains of similar magnitude can also be expected in Cuba, the Cayman Islands, and the Western Bahamas through Wednesday night.


Figure 2. Radar-estimated precipitation since Saturday for the North Carolina/South Carolina border region. Widespread rain amounts of 5 - 10 inches have occurred.


Figure 3. Forecast precipitation for the 5-day period from 8am today through 8am EDT Sunday, October 3, 2010. Image credit: NOAA Hydrometeorological Prediction Center.

Elsewhere in the tropics
Once 96L moves out of the Caribbean, the GFS model predicts that the Western Caribbean will "reload" and produce another tropical disturbance capable of developing into a tropical depression late this week or early next week. The other models are not showing this, but do predict a continuation of the disturbed weather pattern over the Western Caribbean. A second disturbance, if it develops, would be subject to similar steering currents, and may also move northwards across Cuba, Florida, and the Bahamas, then up the U.S. East Coast. This second disturbance might be more dangerous, since it would be dumping heavy rains on regions already drenched by 96L.

Hottest day in Los Angeles history
The mercury hit a blistering 113°F (45.0°C) at 12:15 pm PDT yesterday in downtown Los Angeles, making it the hottest day in Los Angeles history. It may have gotten hotter, but the thermometer broke shortly after the record high was set. The previous record in Los Angeles was 112°F set on June 26, 1990; records go back to 1877. Nearby Long Beach tied its hottest all-time temperature yesterday, with a scorching 111°F. And Christopher C. Burt, our new featured blogger on weather records, pointed out to me that Beverly Hills hit 119°F yesterday--the hottest temperature ever measured in the Los Angeles area, tying the 119°F reading from Woodland Hills on July 22, 2006. Yesterday's record heat was caused by an unusually large and intense upper-level high pressure system centered over Nevada that generated winds blowing from the land to the ocean, keeping the ocean from exerting its usual cooling influence. Remarkably, Los Angeles had its second coldest summer on record this year, and temperatures just five days ago were some the coldest September temperatures in the region for the past 50 years.

The remarkable summer of 2010
Wunderground is pleased to welcome a new featured blogger--weather historian Christopher C. Burt. Chris is a leading expert in the U.S. on weather records, and is author of the world's most popular weather records book published to date, Extreme Weather: A Guide and Record Book. He's spent a lifetime collaborating with like-minded individuals from around the world, and no one--including official sources such as the National Climatic Data Center and the National Extremes Committee--has done as thorough a job correlating the various weather records available and determining the most accurate extreme values of such. Each month he'll be reporting on the notable records for heat, cold, and precipitation set world-wide, and his first post takes a look at the remarkable summer of 2010. It's great to have someone like Chris who stays on top of weather extremes, and I hope you'll pay a visit to his blog and welcome him to the wunderground site!

"Hurricane Haven" airing this afternoon
My live Internet radio show, "Hurricane Haven", will be airing again today at 4pm EDT. The call in number is 415-983-2634, or you can post a question to broadcast@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line.

Today's show will be about 30 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.

I'll have updates as the situation with 96L requires.

Jeff Masters

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797. flsky
Wind picking up here in DBS. Lots of thunder from the SSW, but haven't seen any lighting yet. Hope we don't have another tornado warning.
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Quoting stillwaiting:
For anyone interested i'll be livestreaming on ustream.com in about 20 minutes(handle name is wxjunky)as a nasty squal. Line will be moving in from the se(I live in sarasota,fl) associated w/td16


Sarasota native here. Bee Ridge and McIntosh area. TD16 has a rather large gyre. Expecting rain pretty soon.
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Gonna have to call Press and SJ after work today..
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Quoting tropicfreak:
Good afternoon. I left last night to a 40% chance, now I come home from school with a TD, looks to take a Charley track, except landfall in FL will likely be further south, after that, sitting off the GA coast. However I did see on the track that once it exits FL it will be post-tropical. Do any of you all agree with this and if you are why will it become post-tropical? Nevertheless, it will bring the mid-atlantic some more plentiful rain. The rain event here in Richmond was a bust, we were forecasted to get rain all day yesterday but we had frequent breaks. Most of the rain stayed to the east with the Hampton roads area especially around Norfolk saw continuous rain with frequent downpours as well. Areas west saw more than we did as well, so I guess Richmond is the sandwich in between. We were supposed to see rain today as well especially in the morning but woke up to sunshine. We got at least anywhere from 1.25" to 1.75". Wasn't much compared to how much we were forecasted to get but it helped our drought a little.


At that point that it gets off the coast of GA, it will merge with the frontal boundary across the area, and lose its tropical characteristics (become cold-core)
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Wow, this thing is taking forever to organize ... or pull its arms in. Once it starts, however, this can occur very rapidly. The problem with this one, is that it doesn't have much support upstairs, except on the east side. By "support" I mean high pressure aloft. It's got low pressure over the northwest side.

The only thing that impresses me is the enormous amount of precipitable water this thing carries with it. It's pulling in huge amounts of moisture from the Western Caribbean and the Eastern Pacific.

We've already had rain, rain, rain, setting all time monthly records in some areas of North Carolina. Even if it moves fairly quickly, it's so big that it will still rain for two days, or at least that's the forecast. I've already had to move almost all the plants that I've got in pots outside, under cover, for fear of them drowning.

By the time this thing gets its act together, it may be over Cuba, which means an even broader circulation down the road, because the arms outstretch again. "Big circulation without a dancer" is the phrase of the day.




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In reviewing some RGB satellite imagery, it definitely appears that the center is gradually becoming better defined just south of Isla de la Juventud around 21N and 83W. In the past hour or so, a new convective band has formed to the north and attempting to wrap around the western side. Still continues to lack showers and thunderstorms on the western side, but definitely getting together gradually and could be a tropical storm now.
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Quoting hulazigzag:
The models are now picking up on the trough/front stalling.
What does that mean in regards to TD16?
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Right now I am trying to figure out what my workplaces plans of action are in terms of a possible closing of the plant on Thursday if need be.
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Quoting Hurricanes101:


the 1000mb was right at the center based on the winds, they had it right


Odd because I now have 1000.2 mb and falling rapidly. Either the low is very broad or the heavy convection over us is creating a localised pressure drop.
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Quoting StormChaser81:


I wouldn't say that anymore with the front lifting north. Track may shift west.

If it lifts further enough north it could allow less shear over TD16 and could enforce strengthening.

Not a ton, but more than with the high shear values.


Well I have been having rain all day here on treasure coast.. not to do this with storm I am sure but heck of a lot of rain today in st lucie.
Member Since: August 18, 2008 Posts: 0 Comments: 474
is it me or is td16 looking better on visible
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Quoting StSimonsIslandGAGuy:


Actually the stronger the trough is, and the closer the trough gets to developing a 'negative tilt' the further west the storm will go.
Didnt know that thanks
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Good afternoon. I left last night to a 40% chance, now I come home from school with a TD, looks to take a Charley track, except landfall in FL will likely be further south, after that, sitting off the GA coast. However I did see on the track that once it exits FL it will be post-tropical. Do any of you all agree with this and if you are why will it become post-tropical? Nevertheless, it will bring the mid-atlantic some more plentiful rain. The rain event here in Richmond was a bust, we were forecasted to get rain all day yesterday but we had frequent breaks. Most of the rain stayed to the east with the Hampton roads area especially around Norfolk saw continuous rain with frequent downpours as well. Areas west saw more than we did as well, so I guess Richmond is the sandwich in between. We were supposed to see rain today as well especially in the morning but woke up to sunshine. We got at least anywhere from 1.25" to 1.75". Wasn't much compared to how much we were forecasted to get but it helped our drought a little.
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what winds are the HH finding ???? based on visible images the center is very broad
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The models are now picking up on the trough/front stalling.
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Quoting afj3:

I know. That was the statement I was looking for--someone on the news saying officials would make an announcement later today.


dont be surprised if they r open remmember noel they were open and we were under a Ts warning
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Quoting StSimonsIslandGAGuy:


What is your wind direction?


SSW @ 4mph
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This may be the real thing to watch....

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Quoting will40:
HH dont have SFMR on


yea I think they are trying to get a center fix first
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Quoting StSimonsIslandGAGuy:
The Charleston wx discussion last night talked about the trough getting so deep that it could even get a 'negative tilt' and cause the storm to travel further west. We'll see. But I think I am too far west to get a direct hit.


Front is lifting north StSimons. I do agree you're a little too far W for a direct hit, but if Nicole can wrap some of that convection around you may get some relief.
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Quoting kmanislander:
Rain rate now 1.82 inches per hour !


In the Caymans? Dang
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Quoting BobinTampa:


actually, if you use the XTRAP intensity forecast, it will be a 300MPH storm by then.

Haha, I think that is the first time I've seen the XTRAP intensity used! XP
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Quoting Seastep:


I like this "at-a-glance" chart. Link


Cool! Thank you...1005 when I posted that then.

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Quoting reedzone:
Convection starting to consolidate around the center, this IS organizing at a slow pace.



DMIN and organizing surface circulation and..light shear = slow development for now.. once the sun goes down....boom it goes..potentially
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The COC appears be directly NW of Grand Cayman, between Grand Cayman and the Isle of Youth.
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Quoting StormChaser81:
Seems the front is backing up a little bit.

Check out the moisture plume starting to form over the state.
Link


Exactly what I thought. Also look at water vapor loop.

Thing to watch is the boundary farther west, which seems to be a re-enforcement of dry air *trying* come down to help out the losing front in the battle of Front vs TD16!

For the record, I'm cheering for TD16.
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HH dont have SFMR on
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TD 16 looks to be going almost due N. Is the trough going to be less of an impact than forecasted?
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Quoting kmanislander:


Pressure here now is 1000.4 and falling. TD 16 probably a 995 mb TS


the 1000mb was right at the center based on the winds, they had it right
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Quoting kmanislander:


Pressure here now is 1000.4 and falling. TD 16 probably a 995 mb TS


HWRF was showing 984 yesterday, I wonder.
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Quoting Jax82:
2PM, look at the GFS, hmmmmm



the models are seeing the front eroding. Moisture is moving directly through florida.
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GFS has shifted W in line with the others as well.
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Quoting BobinTampa:


actually, if you use the XTRAP intensity forecast, it will be a 300MPH storm by then.
LOL only if you use the model version!
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756. A4Guy
Quoting smartinwx:
XTRP model shows a Bahamas hit.


Arrrrrgggggh! Scream.
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733:

Sorry, my quote is acting up. Here's the link...

Link

Next run got a 1000.2
Member Since: January 6, 2009 Posts: 0 Comments: 217
If the front is lifting north, will that pull the depression/storm more to the north rather than NE? That would not be good for Florida, IMO.
Member Since: August 14, 2009 Posts: 0 Comments: 471
Rain rate now 1.82 inches per hour !
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Quoting hurricanelover236:
Im gonna be saying i told you so soon. Florida wont get anything but a little rain and a breeze.


I wouldn't say that anymore with the front lifting north. Track may shift west.

If it lifts further enough north it could allow less shear over TD16 and could enforce strengthening.

Not a ton, but more than with the high shear values.
Member Since: August 11, 2008 Posts: 0 Comments: 2315
Quoting CallMeCocoa:
not sure where in brevard you are located, but here in Cocoa, it's been raining since 11:00 a.m. hasn't stop much. i can't tell you how much inches of rain i got, but it's enough to flood some of the road outside my house. lots of lightening, and heavy downpours for 10 mins straight.


Just across the river from you in Merritt Island near the 528. It just started raining about 10 mins ago, and sun finally disappeared about 20 mins ago. Been hearing lots of thunder though, some very close.
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Quoting myrtle1:
nash stop it


myrtle1 its not going to be much worse than this past monday, maybe a little breezier....
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Quoting cat5hurricane:
Without a doubt. I would not be a bit surprised if certain locales pick that up.

If this plays out as currently forecasted, local totals may get really nasty.....really fast.


I simply cannot imagine Market street downtown with over a foot of rain in 24hours.
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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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