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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Hey. Whats up folks? I'll be on here throughout the day here in South Florida tracking Tropical Depression 16. Working on updates right now.
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Quoting nash28:


Not exactly. Even though this will not be a major hurricane rolling through, there will still be the potential for some very hairy weather as it passes. Torrential rain is actually worse than heavy winds.. Not to mention the threat of isolated tornadoes.


If it doesnt start building a east side to the storm, do see Florida getting very much of anything.

But that all depends if the track shifts west. Even with a track shifting west the convection is very displaced on the southeast of the LLC.
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Sorry for the newbie question, but how to you change barometric pressure from inches to mb? It's currently 29.68" at my house west of Orlando, but I'd like to know what it is in mb and be able to calculate that myself. TIA:)
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Quoting StSimonsIslandGAGuy:


Actually that was Hurricane Jeanne (1980) The record rainfall of 23.28" in 24 hours happened November 12-13, 1980.
Thanks SSI- But I don't remember it as a hurricane because there was no wind, just a wall of very heavy rain. Old Age is creeping up on me real fast LOL
Member Since: March 28, 2008 Posts: 0 Comments: 1532
Quoting kmanislander:


only know about Prep but would be surprised if it is not all of them. Have to run now


All public schools are closing at 1pm. Trying to find out about CIS.
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Possible center @ 21.2833N 83.05W.
Member Since: August 14, 2008 Posts: 4 Comments: 4972
Quoting hurricanelover236:
I mean much ado about nothing for florida. Do you agree with that?


Not exactly. Even though this will not be a major hurricane rolling through, there will still be the potential for some very hairy weather as it passes. Torrential rain is actually worse than heavy winds.. Not to mention the threat of isolated tornadoes.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
Quoting MandyFSU:
It's funny that they have TROPICAL STORM SIXTEEN in our forecast this week... right under the clear skies notation.

(I'm in Tallahassee... haven't posted in awhile)


LOL, it's on mine too in SE Alabama.
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Quoting ecflweatherfan:
A nasty batch of storms over Northern and Central Brevard County in FL right now (about 5 miles to my NW right now). A lot of factors in play here. Moisture from TD# 16 moving NNE... stationary front near Daytona Beach, and a moderate to strong seabreeze! Frequent to excessive lightning right now. No rain at my place yet, but it is on the way for sure

Still no rain here either. Kinda hoping it would start and get going so I can go ahead cancel certain plans for tonight....
I am expecting 2 inches or so from this system... much needed!
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Quoting largeeyes:
Link to recon?


Link
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With the GFS, NOGAPS, CMC and HWRF shifting west on 12z, I would suspect the NHC will shift the track ever so slightly on the 5pm..
Member Since: July 11, 2005 Posts: 190 Comments: 16972
12z HWRF comes in just S of Charleston much weaker than the 06z run...

Link
Member Since: July 11, 2005 Posts: 190 Comments: 16972
Quoting nrtiwlnvragn:
12Z GFDL Precip @ 30 hours




HWRF Precip @24 hours



So far HWRF has been consistent on its runs (06Z and 12Z) GFS has shifted some left as well as NOGAPS to be in line with HWRF for the time being.
Member Since: August 14, 2008 Posts: 4 Comments: 4972
A nasty batch of storms over Northern and Central Brevard County in FL right now (about 5 miles to my NW right now). A lot of factors in play here. Moisture from TD# 16 moving NNE... stationary front near Daytona Beach, and a moderate to strong seabreeze! Frequent to excessive lightning right now. No rain at my place yet, but it is on the way for sure
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12Z GFDL Precip @ 30 hours




HWRF Precip @24 hours

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I just took a glance at the local radar. In Key West, we have been cloudy all day a few spits of rain, but nothing. Looking at the radar, it appears all the storm cells are passing us then hitting the trough and piling up just like they were hitting a brick wall!
Member Since: March 28, 2008 Posts: 0 Comments: 1532
Not good Cat5...

That QPF shifted west with the heavy stuff. My backyard would literally turn into a rushing river with 7 inches of rain.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
Yes, all Govt. schools will close at 1pm. And most likely all private schools will follow.

Naturally they couldn't close this morning as no Watches/Warnings were issued until 10am local time.
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Link to recon?
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Backing off rainfall totals every so slightly...
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NOGAPS 12Z COMPLETE RUN
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Quoting weatherbro:


Not to mention that trough is supposed to break down the Bermuda ridge by next week. So other then that, the steering currents are pretty much the same.


Which yeah, by looking at it, is the reason that the next possible development initially moves to the North, then back to the WNW for a brief period, then back to the N then NNE. Shows a very brief ridge develop, all to get destroyed by the next trough... opening the doors to another east coast slider
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Quoting nash28:


Disagree. I don't think torrential rains threatening an area that is already way saturated is considered much ado about nothing. Throw 50-60mph winds into that equation, and it can/will make for an ugly day and potentially dangerous.


50/60 mph winds plus saturated ground= a very very bad day. I have the feeling that down home along the coast of NC the powers going to be going out for a lot of people. The ground is like quicksand in some places my family's been saying.
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Quoting stormpetrol:
The weather here looks nasty and rainy, quite a bit of wave action on the SW side of Island but very little wind , I suspect that's because they are out of the SSW/SW, I think once the storm gets ENE of us we will feel lot more wind.


looking at the webcam and it seems 7 Mile Beach is getting slammed right now!
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Did somebody see the 12Z NOGAPS! The tropical altantic could wake up significantly with a possible new parade of storms...
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Quoting hurricanelover236:
i hate to say ut but "Nicole" is all much ado about nothing. Does any one else here agree?


Disagree. I don't think torrential rains threatening an area that is already way saturated is considered much ado about nothing. Throw 50-60mph winds into that equation, and it can/will make for an ugly day and potentially dangerous.
Member Since: July 11, 2005 Posts: 190 Comments: 16972
Quoting StSimonsIslandGAGuy:


Will you go stormchasing? Or not go cause it's the middle of the week?


No because of classes. Most are planning midterms after fall break next week so they are cramming test material. Which I might just be able to walk around campus and storm chase if we get anymore rain. We were so close to flooding yesterday.
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1001 mb so far from recon
i hate to say ut but "Nicole" is all much ado about nothing. Does any one else here agree?
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Quoting ecflweatherfan:


That high will be a surface High. Mid level and upper level trough expected to persist over the eastern CONUS for the next several days. In other words, the same steering level winds are supposed to persist over the region for several days.


Not to mention that trough is supposed to break down the Bermuda ridge by next week. So other then that, the steering currents are pretty much the same.
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Gulf and Tropics (Updated every ~1/2 hour)

Animated Low Cloud Loop
Member Since: July 3, 2005 Posts: 424 Comments: 128259
NEXRAD Radar
Key West, Base Reflectivity 0.50 Degree Elevation Range 248 NMI


Member Since: July 3, 2005 Posts: 424 Comments: 128259
Quoting chrisdscane:


correct i was saying that earlyer


I just got on really fast before I go to my special topcis in meteorology class. That class is pretty much all the math in meteorology. Anyway was posting my first thoughts.
But here are my second thoughts. Although they say the front and developing nor'easter off the east coast will absorb the tropical depression I think it could be more like nor'Ida where the depression takes over. If this happens I expect around a 60mph storm (Extratropical) around the Carolinas Thursday.
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Quoting kmanislander:


only know about Prep but would be surprised if it is not all of them. Have to run now
Ok. TTYL
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TD16's central pressing must has fallen below 1000mb
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The weather here looks nasty and rainy, quite a bit of wave action on the SW side of Island but very little wind , I suspect that's because they are out of the SSW/SW, I think once the storm gets ENE of us we will feel lot more wind.
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Quoting stormwatcherCI:
Do you know if government schools are closing too ? My grandson lives with me and I didn't even bother sending him since I work in East End at the P.O. by myself so wouldn't be able to go pick him up. Walkers Road is always a mess when it rains and then with the traffic. I don't envy you at all.


only know about Prep but would be surprised if it is not all of them. Have to run now
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TD16 moved .3N according to the latest coordinates. No easterly component yet...
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I question the 1000 mb estimate as we have 1000.7 here and we are about 80 miles away from the center.
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Quoting kmanislander:
1000.7 mb and still falling


Interesting weather there for sure :)
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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.