An Active Atlantic Hurricane Season Still Predicted by NOAA, CSU, and TSR

By: Dr. Jeff Masters , 4:07 PM GMT on August 09, 2013

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As we stand on the cusp of the peak part of hurricane season, all of the major groups that perform long-range seasonal hurricane forecasts are still calling for an active 2013 Atlantic hurricane season. NOAA forecasts an above-normal and possibly very active Atlantic hurricane season in 2013, in their August 8 outlook. They give a 70% chance of an above-normal season, a 25% chance of an near-normal season, and 5% chance of a below-normal season. They predict a 70% chance that there will be 13 - 19 named storms, 6 - 9 hurricanes, and 3 - 5 major hurricanes, with an Accumulated Cyclone Energy (ACE) 120% - 190% of the median. If we take the midpoint of these numbers, NOAA is calling for 16 named storms, 7.5 hurricanes, 4 major hurricanes, and an ACE index 155% of normal. This is well above the 1981 - 2010 average of 12 named storms, 6 hurricanes, and 3 major hurricanes. Hurricane seasons during the active hurricane period 1995 - 2012 have averaged 15 named storms, 8 hurricanes, and 4 major hurricanes, with an ACE index 151% of the median.


Figure 1. Tropical Storm Dorian on July 25, 2013, when the storm reached peak intensity--sustained winds of 60 mph. Formation of early-season tropical storms like Chantal and Dorian in June and July in the deep tropics is usually a harbinger of an active Atlantic hurricane season. Image credit: NASA.

NOAA cites five main reasons to expect an active remainder of hurricane season:

1) Sea Surface Temperatures (SSTs) are above average in the Main Development Region (MDR) for hurricanes, from the coast of Africa to the Caribbean. As of August 9, SST were 0.4°C (0.8°F) above average.
2) Trade winds are weaker than average across the MDR, which has caused the African Monsoon to grow wetter and stronger, the amount of spin over the MDR to increase, and the amount of vertical wind shear to decrease.
3) No El Niño event is present or expected this fall.
4) There have been two early-season tropical storms in the deep tropics (Tropical Storms Chantal and Dorian), which is generally a harbinger of an above-normal season.
5) We are in an active hurricane period that began in 1995.

Colorado State predicts a much above-average hurricane season
A much above-average Atlantic hurricane season is on tap for 2013, according to the seasonal hurricane forecast issued August 2 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 18 named storms, 8 hurricanes, and 3 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 142. The forecast calls for an above-average chance of a major hurricane hitting the U.S., both along the East Coast (40% chance, 31% chance is average) and the Gulf Coast (40% chance, 30% chance is average). The risk of a major hurricane in the Caribbean is also above average, at 53% (42% is average.)

Analogue years
The CSU team picked five previous years when atmospheric and oceanic conditions were similar to what we are seeing this year: cool neutral ENSO conditions and slightly above-average tropical Atlantic sea surface temperatures. Those five years were 2008, a very active year with 16 named storms and 4 major hurricanes--Gustav, Ike, Paloma, and Omar; 2007, an active year with 15 named storms and two Category 5 storms--Dean and Felix; 1996, an above average year with 13 named storms and 6 major hurricanes--Edouard, Hortense, Fran, Bertha, Isidore, and Lili; 1966, an average year with 11 named storms and 3 major hurricanes--Inez, Alma, and Faith; and 1952, a below average year with 7 named storms and 3 major hurricanes. The average activity during these five analogue years was 12.4 named storms, 7.2 hurricanes, and 3.8 major hurricanes.

TSR predicts an above-average hurricane season: 14.8 named storms
The August 6 forecast for the 2013 Atlantic hurricane season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) calls for an active season with 14.8 named storms, 6.9 hurricanes, 3 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 121. The long-term averages for the past 63 years are 11 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 103. TSR rates their skill level as good for these August forecasts--47% - 59% higher than a "no-skill" forecast made using climatology. TSR predicts a 58% chance that U.S. land falling activity will be above average, a 26% chance it will be near average, and a 16% chance it will be below average. They project that 4 named storms will hit the U.S., with 1.8 of these being hurricanes. The averages from the 1950-2012 climatology are 3.1 named storms and 1.4 hurricanes. They rate their skill at making these August forecasts for U.S. landfalls just 9% - 18% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.4 named storms, 0.6 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR's two predictors for their statistical model are the forecast July - September trade wind speed over the Caribbean and tropical North Atlantic, and the forecast August - September 2013 sea surface temperatures in the tropical North Atlantic. Their model is calling for warmer than average SSTs and near average trade winds during these periods, and both of these factors should act to increase hurricane and tropical storm activity.


Figure 2. Comparison of the percent improvement over climatology for May and August seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 1999-2009 (May) and 1998-2009 (August), using the Mean Squared Error. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.


Figure 3. Comparison of the percent improvement in mean square error over climatology for seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 2003-2012, using the Mean Square Skill Score (MSSS). The figure shows the results using two different climatologies: a fixed 50-year (1950 - 1999) climatology, and a 2003 - 2012 climatology. Skill is poor for forecasts issued in December and April, moderate for June forecasts, and good for August forecasts. Image credit: Tropical Storm Risk, Inc.

FSU predicts an above-average hurricane season: 15 named storms
The Florida State University (FSU) Center for Ocean-Atmospheric Prediction Studies (COAPS) issued their fifth annual Atlantic hurricane season forecast on May 30, calling for a 70% probability of 12 - 17 named storms and 5 - 10 hurricanes. The mid-point forecast is for 15 named storms, 8 hurricanes, and an accumulated cyclone energy (ACE) of 135. The scientists use a numerical atmospheric model developed at COAPS to understand seasonal predictability of hurricane activity. The model is one of only a handful of numerical models in the world being used to study seasonal hurricane activity and is different from the statistical methods used by other seasonal hurricane forecasters such as Colorado State, TSR, and PSU (NOAA uses a hybrid statistical-dynamical model technique.) The FSU forecast has been one of the best ones over the past four years:

2009 prediction: 8 named storms, 4 hurricanes. Actual: 9 named storms, 3 hurricanes
2010 prediction: 17 named storms, 10 hurricanes. Actual: 19 named storms, 12 hurricanes
2011 prediction: 17 named storms, 9 hurricanes. Actual: 19 named storms, 7 hurricanes
2012 prediction: 13 named storms, 7 hurricanes. Actual: 19 named storms, 10 hurricanes

Penn State predicts an above-average hurricane season: 16 named storms
A statistical model by Penn State's Michael Mann and alumnus Michael Kozar is calling for an active Atlantic hurricane season with 16 named storms, plus or minus 4 storms. Their prediction was made using statistics of how past hurricane seasons have behaved in response to sea surface temperatures (SSTs), the El Niño/La Niña oscillation, the North Atlantic Oscillation (NAO), and other factors. The statistic model assumes that in 2013 the May 0.87°C above average temperatures in the MDR will persist throughout hurricane season, the El Niño phase will be neutral to slightly warm, and the North Atlantic Oscillation (NAO) will be near average.

The PSU team has been making Atlantic hurricane season forecasts since 2007, and these predictions have done pretty well, except for in 2012, when an expected El Niño did not materialize:

2007 prediction: 15 named storms, Actual: 15
2009 prediction: 12.5, named storms, Actual: 9
2010 prediction: 23 named storms, Actual: 19
2011 prediction: 16 named storms, Actual: 19
2012 prediction: 10.5 named storms, Actual: 19

UK Met Office predicts a slightly above-average hurricane season: 14 named storms
The UKMET office forecast for the 2013 Atlantic hurricane season, issued May 13, calls for slightly above normal activity, with 14 named storms, 9 hurricanes, and an ACE index of 130. In contrast to the statistical models relied upon by CSU, TSR, and NOAA, the UKMET model is done strictly using two dynamical global seasonal prediction systems: the Met Office GloSea5 system and ECMWF system 4. In 2012, the Met Office forecast was for 10 tropical storms and an ACE index of 90. The actual numbers were 19 named storms and an ACE index of 123.


Figure 4. Total 2013 Atlantic hurricane season activity as predicted by twelve different groups.

NOAA predicts a below-average Eastern Pacific hurricane season
NOAA's pre-season prediction for the Eastern Pacific hurricane season, issued on May 23, calls for a below-average season, with 11 - 16 named storms, 5 - 8 hurricanes, 1 - 4 major hurricanes, and an ACE index 60% - 105% of the median. The mid-point of these ranges gives us a forecast for 13.5 named storms, 6.5 hurricanes, and 2.5 major hurricanes, with an ACE index 82% of average. The 1981 - 2010 averages for the Eastern Pacific hurricane season are 15 named storms, 8 hurricanes, and 4 major hurricanes.

NOAA predicts a below-average Central Pacific hurricane season
NOAA's pre-season prediction for the Central Pacific hurricane season, issued on May 22, calls for a below-average season, with 1 - 3 tropical cyclones. An average season has 4 - 5 tropical cyclones, which include tropical depressions, tropical storms, and hurricanes. Hawaii is the primary land area affected by Central Pacific tropical cyclones.

West Pacific typhoon season forecast not available this year
Dr. Johnny Chan of the City University of Hong Kong usually issues a seasonal forecast of typhoon season in the Western Pacific, but did not do so in 2012 or 2013. An average typhoon season has 27 named storms and 17 typhoons. Typhoon seasons immediately following a La Niña year typically see higher levels of activity in the South China Sea, especially between months of May and July. Also, the jet stream tends to dip farther south than usual to the south of Japan, helping steer more tropical cyclones towards Japan and Korea.

Quiet in the Atlantic this weekend
There are no Atlantic threat areas to discuss today, and none of the reliable models for tropical cyclone formation is predicting development during the coming seven days. However, there are some indications that the atmosphere over the tropical Atlantic will become more conducive for tropical storm formation beginning around August 15. The Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days, may move into the Atlantic then, increasing tropical storm formation odds. At the same time, the computer models are indicating an increase in moisture over the tropical Atlantic, due to a series of tropical waves expected to push off of the coast of Africa. There will also be several eastward-moving Convectively-Coupled Kelvin Waves (CCKWs) traversing the Atlantic during that period. These atmospheric disturbances have a great deal of upward-moving air, which helps strengthen the updrafts of tropical disturbances. Formation of the Eastern Pacific's Hurricane Gil and Henriette were aided by CCKWs. These same CCKWs will cross into the Atlantic and increase the odds of tropical storm formation during the period August 15 - 20.

Have a great weekend, everyone!

Jeff Masters

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1190. Grothar
Quoting 1188. redwagon:


Chrome crashed and burned on me, re-downloaded and installed, still trashed, having to use explorer, ick.

Sure wish that GOM ULL could find a way to the surface but I deeply admire how it's sucking up moisture to sling onto TX tomorrow and the next day.

104o yesterday, no clouds, 100s are way more bearable with cloud cover.


Chrome crashed on me and then Firefox.
Member Since: July 17, 2009 Posts: 71 Comments: 26153
1189. TxLisa
Quoting 1161. LargoFl:
yes we had a very bad storm here by me last night..my dogs were scared also..3000 lightning strikes an hour whew...well hopefully the rains by you the next few days will help with the drought there..you folks really need the rains huh.
We sure do! I jjust got back from my grandmother's home in up East Texas (Laneville, Texas). Everything is parched! Crops and grass are all dead. Some how my cousin manages to keep his herd of cattle fed. Rain will be a welcome sight! Thanks for the maps and updates:)
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Quoting 1154. Sfloridacat5:
Test - can't seem to get into the blog.


Chrome crashed and burned on me, re-downloaded and installed, still trashed, having to use explorer, ick.

Sure wish that GOM ULL could find a way to the surface but I deeply admire how it's sucking up moisture to sling onto TX tomorrow and the next day.

104o yesterday, no clouds, 100s are way more bearable with cloud cover.
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Skye, Baha, TS - take a look at post #1156, and tell me what I'm missing? Late in the month, notice the MJO forecast quickly transitioning to a strong upward pulse in the eastern Pacific. If that is the case, and we based development strictly on the MJO, we could be looking at ideal moisture conditions and activity in the Atlantic basin as we roll towards the peak of season.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
It is however being enhanced by an ULL to its north.

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Jenna sure is pregnant!!!
Member Since: October 3, 2008 Posts: 0 Comments: 5864
Quoting 1163. hurricanes2018:
something is spinning in the red!
That may be our catalyst for development in the Western Caribbean.
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1183. TxLisa
Quoting 1172. Houstonweathergrl:
TxLisa I am on the east side of Houston and not a drop. But there are clouds so I remain hopeful.
I live right by Ellington Field in Clear Lake area hopefully its drifting your way:)
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1182. LargoFl
just a lot of rain out there.............
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Quoting 993. SuperStorm093:
Wow, another run of the GFS to me looking to come in very boring, you guys have to really think how both the EURO and GFS are completely wrong, and I find that hard to be.
Really... I'm still trying to figure out how what u say about the boring GFS run contradicts what people have been saying about no major activity before the 15th or 20th of the month....

Really... we're not at all disputing the current quiet period, just your contention that said period is automatically equivalent to a quiet season number / ACE - wise...

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We should start to see something trying to consolidate within the next 3-5 days.



The GFS would also tend to agree with that.

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Quoting 1163. hurricanes2018:
something is spinning in the red!


Its in the UPPER LEVELS NOTHING at the surface at all.....I just checked the winds on all the islands.....ALL out of the EAST....NOTHING there but a spin in the upper levels.
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1178. LargoFl
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Utor now up to a 105 MPH Category 2 Typhoon.
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1176. LargoFl
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FIM-8 shows landfall near the upper Texas coast:



PWAT looking good right near the coast.



Some 5-10 inch rains on the total precip. through 14 days.

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1174. Skyepony (Mod)
dvorak has UTOR at 989.6mb, 59kts with a T# 3.7 Weakening flag was throw but the Raw T is just starting to go up. Has a Uniform Central Dense Overcast..
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Quoting 1162. Sfloridacat5:
Looks like the NAM and GFS are pretty much in agreement that somethings going to form in the Caribbean in about 4 days.
May also have something to do with Kelvin and MJO since they arrive there first. Not sure if the computers know that or not.
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TxLisa I am on the east side of Houston and not a drop. But there are clouds so I remain hopeful.
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UTOR's eye looks like its about to clear out.



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1170. JRRP
Quoting hurricanes2018:
something is spinning in the red!

ULL
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1169. Skyepony (Mod)
MIMIC of UTOR~ tiny CDO..
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Quoting 1148. PalmBeachWeather:
With the high humidity, and high temperatures...August must be a tough time to wear a paper bag over your head...Just askin'
No paper bags..except when the teams is terrible.
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1167. JRRP
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1166. LargoFl
models aren't picking up on anything developing today tropical wise.........
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Quoting 1159. seer2012:

I suspect the wave train will get busy when all that moisture that is pouring across the Arabian Sea and Indian Ocean hits Africa and starts getting heated up over land. It appears to be about a week away.
Kelvin and mjo on will be coming.
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1164. ncstorm
NOAA NWS National Hurricane Center
NHC is monitoring an area of cloudiness and thunderstorms that has formed over the western Gulf of Mexico, associated with a trough of low pressure. Development - if any - will be slow to occur before it moves inland over northeastern Mexico on Sunday.
It has a low chance of becoming a tropical cyclone during the next 48 hours and five days.
Elsewhere, there are no other area of disturbed weather that have any potential for tropical cyclone development during the next five days.
Get the latest on the tropics anytime by visiting the NHC website at www.hurricanes.gov
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something is spinning in the red!
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Looks like the NAM and GFS are pretty much in agreement that somethings going to form in the Caribbean in about 4 days.
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1161. LargoFl
Quoting 1158. TxLisa:
It is actually raining right now in Houston!The thunder scared my dogs. It's been so long since they have heard it:)
yes we had a very bad storm here by me last night..my dogs were scared also..3000 lightning strikes an hour whew...well hopefully the rains by you the next few days will help with the drought there..you folks really need the rains huh.
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1160. Skyepony (Mod)
Aqua pass of UTOR earlier..
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Quoting 1145. unknowncomic:
Lets not forget that when wave train really gets going soon, the early waves moisten the environment for the next waves. What may seem to be terrible conditions changes to better conditions because of that.
Also, a "switch" usually turns on in the near future. Even naked swirls can develop.

I suspect the wave train will get busy when all that moisture that is pouring across the Arabian Sea and Indian Ocean hits Africa and starts getting heated up over land. It appears to be about a week away.
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1158. TxLisa
Quoting 1142. LargoFl:
Nam has rain for Texas Monday....................
It is actually raining right now in Houston!The thunder scared my dogs. It's been so long since they have heard it:)
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I'm starting a fall severe wx season / general fall wx outlook for a another page i have.

If anyone has anything they've noticed that would effect either or any other opinions or observations, please wu-mail them to me..

It could be something like just your best guess or something having to do with a real anomaly like say temp, or rainfall, or geo-potential height or soi.


Thanks You Guys Very Much,
GS




PS GO BRAVES....
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Quoting 1140. bigwes6844:




Good post. It indicates the MJO initially entering the Atlantic basin with a weak pulse and similarly associated moisture. And, further into the month as it progresses eastwards, the pulse becomes more amplified as it nears the African coast; but, what catches my eye is the continued propagation forecast with a stronger ascending pulse in the eastern Pacific as we head into September. That may indicate that we see some activity in the next couple of weeks, a brief lull, and then as this stronger upward pulse enters the Caribbean in September, we may see prime moisture conditions for development there, and then likely further eastwards in the MDR as it interacts with the twaves rolling off the African coast near the very heart of the season.
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1155. ncstorm
precip totals for the CMC

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Test - can't seem to get into the blog.
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1153. hydrus
Quoting 1109. PensacolaDoug:
G'morning all. Nothing coming to P'cola? It's a beautiful thing!
This is true. Florida is a great place when not ripped to pieces by hurricanes.
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What's wrong with the site? It's doing weird things.
Also, I was refused entry into the site with some message saying the site was too full/crowded (or something like that)

That's scary on a Saturday morning with no named storms.
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1151. ncstorm
Good Morning WU..big rain event setting up for the eastern US..precip total up to 384 hours..the models have been showing nothing but multiple lows exiting off the SE coast..

00z GFS
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I got a notice that said "Site is overloaded, try back in a few minute" Never , ever have seen that before.
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Seems to be some rotation in the weather that is still over land.
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Quoting 1145. unknowncomic:
Lets not forget that when wave train really gets going soon, the early waves moisten the environment for the next waves. What may seem to be terrible conditions changes to better conditions because of that.
Also, a "switch" usually turns on in the near future. Even naked swirls can develop.
With the high humidity, and high temperatures...August must be a tough time to wear a paper bag over your head...Just askin'
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1147. LargoFl
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1146. hydrus
Quoting 1131. Autistic2:
WOW, I killed the blog with just one question?
Will you be charged with blogkilling.?..:)
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Lets not forget that when wave train really gets going soon, the early waves moisten the environment for the next waves. What may seem to be terrible conditions changes to better conditions because of that.
Also, a "switch" usually turns on in the near future. Even naked swirls can develop.
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Quoting 1136. mikatnight:
Good Morning!

8:07 am (12:07 GMT)

Workers at the new Lantana bridge go over the final details before the paving process, which is set to begin Monday.


Blasted paparazzi! It's getting to where I can't even pee without a flashbulb going off! (sigh) Being a celebrity has its downside...

While Grothar's blob certainly delivered rain across the state yesterday, all we got was a whopping 0.01". Today and tomorrow are supposed to be sunny, clear and hot.

Busy morning, late start...check back in later. Have a great day everyone!
Mik....I see you are standing in front of Kona Bay Cafe...Pretty good breakfast...Service can be iffy,..
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1143. LargoFl
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1142. LargoFl
Nam has rain for Texas Monday....................
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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.