July hurricane outlook

By: Dr. Jeff Masters , 7:26 PM GMT on July 02, 2009

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Atlantic tropical cyclone activity typically picks up a bit during the first half of July. Since the current active hurricane period began in 1995, seven of 14 years (50%) have had a named storm form during the first half of July. The busiest first half of July occurred in 2005, when three hurricanes formed. These included Hurricane Dennis and Hurricane Emily--the strongest hurricanes ever observed so early in the season. As seen in Figure 1, most of the early July activity occurs in the Gulf of Mexico, Western Caribbean, and Carolina waters. However, a few long-track "Cape Verdes" hurricanes begin to occur. These are spawned by tropical waves that come off the coast of Africa. Tropical waves serve as the instigators of about 85% of all major hurricanes. Last year's Hurricane Bertha was one such rare early July Cape Verdes hurricane. Bertha's 120 mph winds made it the sixth strongest early-season Atlantic hurricane on record. Bertha also set the record for farthest east formation as a tropical storm, hurricane, and major hurricane, so early in the season.


Figure 1. Tracks of all tropical storms and hurricanes 1851 - 2006 that formed July 1-15. North Carolina and the Gulf of Mexico coast from the Florida Panhandle to Texas are the preferred strike locations. Oddly, the Florida Peninsula has been struck by only two storms that formed in the first half of July.

Sea Surface Temperatures
Sea Surface Temperatures (SST) anomalies have warmed slightly over the past two weeks, but are close to average over the tropical Atlantic between Africa and Central America (Figure 2). These are the are the coolest SST anomalies we've seen since 1994. The strength of the Azores-Bermuda high has been near average over the past two weeks, driving near-average trade winds. Stronger-than-average trade winds were observed through most of the period November 2008 - May 2009, which helped cool the tropical Atlantic substantially. Strong winds mix up colder water from the depths and cause greater evaporative cooling. The latest 2-week run of the GFS model predicts continued average-strength trade winds through mid-July, so SSTs should remain near average during this period.

Typically, July tropical storms form over the Gulf of Mexico, Western Caribbean, and Gulf Stream waters just offshore Florida. SSTs are about 1.0°C above average for this time of year in the Gulf of Mexico, but near average elsewhere. July storms typically form when a cold front moves off the U.S. coast and stalls out, with the old frontal boundary serving as a focal point for development of a tropical disturbance. There will be one or two fronts moving off the U.S. coast over the next two weeks, and we will need to watch these for development. Wind shear is too high and SSTs are usually too cold in July to allow African tropical waves to develop into tropical storms. African tropical waves serve as the instigators of about 85% of all major hurricanes,

Figure 2. Sea Surface Temperature (SST) departure from average for July 2, 2009. SSTs were near average over the tropical Atlantic's Main Development region for hurricanes, from Africa to Central America between 10° and 20° North Latitude. Note the large region of above average SSTs along the Equatorial Pacific off the coast of South America, the hallmark of a developing El Niño episode. Image credit: NOAA/NESDIS

El Niño
El Niño conditions continue to amplify over the tropical Eastern Pacific. Ocean temperatures there rose 0.5°C over the past two weeks, and are now 0.45°C above the threshold for El Niño, according to the Australian Bureau of Meteorology (Figure 3). NOAA's Climate Prediction Center issued an El Niño Watch in early June, saying "that conditions are favorable for a transition from neutral to El Niño conditions during June - August 2009". The pattern of changes in surface winds, upper-level winds, sea surface temperatures, and deeper water heat content are all consistent with what has been observed during previous developing El Niños, and latest set of mid-June runs of the El Niño computer models are almost universally calling for El Niño conditions to become well-established for the peak months of hurricane season, August - October. It is likely that Atlantic hurricane activity will be suppressed in 2009 due to the strong upper-level winds and resulting wind shear an El Niño event usually brings to the tropical Atlantic.


Figure 3. Sea Surface Temperature (SST) departure from average for the the equatorial Eastern Pacific (the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region"). El Niño conditions exist when the SST in this region rises 0.5°C above average. As of June 28, 2009, SSTs in the Niño 3.4 region had risen to 0.95°C above average. To be considered an "El Niño episode", El Niño conditions must occur for five consecutive months, using 3-month averages. Image credit: Australian Bureau of Meteorology.

Wind shear
Wind shear is usually defined as the difference in wind between 200 mb (roughly 40,000 foot altitude) and 850 mb (roughly 5,000 foot altitude). In most circumstances, wind shear above 20 knots will act to inhibit tropical storm formation. Wind shear below 12 knots is very conducive for tropical storm formation. High wind shear acts to tear a storm apart. The jet stream's band of strong high-altitude winds is the main source of wind shear in July over the Atlantic hurricane breeding grounds, since the jet is very active and located quite far south this time of year.

The jet stream over the past two months has been locked into a pattern where a southern branch (the subtropical jet stream) brings high wind shear over the Caribbean, and a northern branch (the polar jet stream) brings high wind shear offshore of New England. This often leaves a "hole" of low shear between the two branches off the coast of North Carolina, which is where Tropical Depression One formed at the end of May.

The jet stream is forecast (Figure 4) to maintain this two-branch pattern over the coming two weeks. This means that the waters offshore of the Carolinas are the most likely place for a tropical storm to form during this period.


Figure 4. Wind shear in m/s between 200 mb and 850 mb, as forecast by the 06Z July 02, 2009 run of the GFS model. The position and strength of the subtropical jet stream is forecast to change little over the next two weeks, and this jet will bring high wind shear to the Caribbean and Gulf of Mexico into mid-July. There will at times be a region of low shear between the polar jet (northern set of arrows on the plots) and the subtropical jet, allowing for possible tropical development off the coast of North Carolina. Wind speeds are given in m/s; multiply by two to get a rough conversion to knots. Thus, the red regions of low shear range from 0 - 16 knots.

Dry air and African dust
June and July are the peak months for dust coming off the coast of Africa, and the Saharan dust storms have been quite active over the past month. Expect dust from Africa to be a major deterrent to any storms that try to form between Africa and the Lesser Antilles Islands in July.

Steering currents
The steering current pattern over the past few weeks has not changed much, and is typical for June and July. We have an active jet stream bringing many troughs of low pressure off the East Coast of the U.S. These troughs are frequent enough and strong enough to recurve any tropical storms or hurricanes that might penetrate north of the Caribbean Sea. Steering current patterns are predictable only about 3 - 5 days in the future, although we can make very general forecasts about the pattern as much as two weeks in advance. At present, it appears that the coming two weeks will maintain the typical July pattern, bringing many troughs of low pressure off the East Coast capable of recurving any July storms that might form. There is no telling what might happen during the peak months of August, September, and October--we might be in for a repeat of the favorable 2006 steering current pattern that recurved every storm out to sea--or the unfavorable 2008 pattern, that steered Ike and Gustav into the Gulf of Mexico.

Summary
Recent history suggests a 50% chance of a named storm occurring in the first half of July. Given that none of the computer models are forecasting tropical storm formation in the coming seven days, and SST and wind shear patterns look pretty average, I'll go with a 20% chance of a named storm forming during the first half of July.

Vote for Mike Theiss as an Antarctica blogger
Extreme weather photographer Mike Theiss, who wrote our Ultimate Chase photography blog for two years until a new job took him to South America, wants your help. He's entering a Quark Expeditions competition to receive an expense-paid 2-week trip to Antarctica, where he will do some intensive photography and blogging. In order to go, he needs the votes to show that he's a popular blogger. So, if you liked his posts while he was blogging for wunderground, and want to see him blog for wunderground during this potential Antarctica voyage, go to http://www.blogyourwaytoantarctica.com/blogs/view /220 and cast a vote. It takes about 3 minutes navigate through the registration and voting process. Mike will be back chasing hurricanes this August, and has promised to post his excellent storm photos on wunderground should we help him secure the Antarctica gig.

Have a great holiday weekend, and I'll be back Monday with a new post.

Jeff Masters

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1447. KEEPEROFTHEGATE (Mod)
heres a movie to watch

Link
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Hey kids - i don't have much time - on the hotel computer - we are staying overnight just outside of little rock ark and headed for new mex tomorrw. Anything we should be worried about?

Not many miles behind us - I am a bit older than I thought apparently
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a little news on El Nino


Daniel Swain Says:
July 3rd, 2009 at 2:46 pm

Lots to discuss on the El Nino front. El Nino is effectively here, although sst anomalies have to persist for another month or two to make it official. There is an increasingly high indication that this El Nino will have significant effects on CA, at least next winter. More later…perhaps next week once the June SSTs have been ingested into the models and a new outlook is issued
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Tropicfreak, that water spout pic is in Jacksonville a few days ago, accoding to the source.
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Quoting KEEPEROFTHEGATE:


well bye bye 94 on to 95L next


Where and when do you think 95L will come upon us?
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1442. KEEPEROFTHEGATE (Mod)
Quoting AllStar17:


Keeper....any development?


not at the moment real quiet
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EP 94 2009070500 BEST 0 157N 1060W 25 1008 DB
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1440. KEEPEROFTHEGATE (Mod)
naw you won't get banned
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Quoting beell:
1432.
Warts and all, nrt-don't you just love it!
Thanks, and a Happy 4th.


Happy Independence Day. I'll probably get banned, but I'll take it today.
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1438. KEEPEROFTHEGATE (Mod)
Quoting nrtiwlnvragn:
invest_DEACTIVATE_al942009.ren


well bye bye 94 on to 95L next
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Quoting nrtiwlnvragn:
invest_DEACTIVATE_al942009.ren


Not a surprise at all.
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1436. beell
1432.
Warts and all, nrt-don't you just love it!
Thanks, and a Happy 4th.
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invest_DEACTIVATE_al942009.ren
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1434. Makoto1
lol You couldn't have picked a more perfect time to show that video.

John Mellencamp is one of the three coming for a concert up here in Dayton Friday.

94E might take a couple of days to really get together but it's definitely working on it now.
Quoting AllStar17:
Taz,

What do you think about the tropical wave in the Central Caribbean. Keeper put a center fix at 15 n 73 w. If it were to get into a more favorable environment, with shear expected to lessen, is development possible?



yes
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Taz,

What do you think about the tropical wave in the Central Caribbean. Keeper put a center fix at 15 n 73 w. If it were to get into a more favorable environment, with shear expected to lessen, is development possible?
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Quoting btwntx08:
got good news its cooling off lol
Hearne, Texas (Airport)
Updated: 6:25 P.M
118 °F
Scattered Clouds
Dew Point: 83 °F
Pressure: 29.85 in (Steady)
Heat Index: 150 °F



Is that a personal weather station or an official one? In the sun or shade?

Then again...does it matter? My temp gauge read 101 today and it is on my porch under the shade. Texas is baking!
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Quoting KEEPEROFTHEGATE:


cen fix
15n/73w


Keeper....any development?
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Quoting AllStar17:
No surprise here, either. I expected them to up the chances to medium as 94E gets better organized.

000
ABPZ20 KNHC 042337
TWOEP
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
500 PM PDT SAT JUL 4 2009

FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

AN AREA OF LOW PRESSURE LOCATED ABOUT 275 MILES SOUTH-SOUTHWEST OF
MANZANILLO MEXICO CONTINUES TO BECOME BETTER ORGANIZED...ALTHOUGH
THE ASSOCIATED THUNDERSTORM ACTIVITY REMAINS LIMITED AND NOT
CONCENTRATED NEAR THE CENTER. UPPER-LEVEL WINDS ARE BECOMING MORE
FAVORABLE FOR ADDITIONAL DEVELOPMENT OVER THE NEXT COUPLE OF DAYS
AS THIS SYSTEM MOVES WEST-NORTHWESTWARD AROUND 10 MPH. THERE IS A
MEDIUM CHANCE...30 TO 50 PERCENT...OF THIS SYSTEM BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER BERG

Not looking too bad, center slowly but steadily consolidating and bands forming, and good outflow. Very large system.







you where right theres now a MEDIUM CHANCE for 94E
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Acemmett90--

94L certainly does look like crap. But 94E is slowly but steadily getting better organized, and does not look like crap. The NHC has upped the development chances to medium (30-50 %)
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I see that,it looks like its moving around the periphery of the High pressure ridge..
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Expect 94L to be deactivated soon and the NHC no longer mention it in the TWO.
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Interestingly enough the circulation of 94L continues to move south. But, the NHC stubbornly is continuing to say it is moving east, when it is not. The convection is, but the center is most certainly not.
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1421. Makoto1
Quoting btwntx08:
got good news its cooling off lol
Hearne, Texas (Airport)
Updated: 6:25 P.M
118 °F
Scattered Clouds
Dew Point: 83 °F
Pressure: 29.85 in (Steady)
Heat Index: 150 °F



rofl It sure is.

I just noticed by the end of next week we might be in the lower 90's. Not looking forward to that...

And it hurts to see 94L, it looks unimportant to say the least.
No surprise here, either. I expected them to up the chances to medium as 94E gets better organized.

000
ABPZ20 KNHC 042337
TWOEP
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
500 PM PDT SAT JUL 4 2009

FOR THE EASTERN NORTH PACIFIC...EAST OF 140 DEGREES WEST LONGITUDE..

AN AREA OF LOW PRESSURE LOCATED ABOUT 275 MILES SOUTH-SOUTHWEST OF
MANZANILLO MEXICO CONTINUES TO BECOME BETTER ORGANIZED...ALTHOUGH
THE ASSOCIATED THUNDERSTORM ACTIVITY REMAINS LIMITED AND NOT
CONCENTRATED NEAR THE CENTER. UPPER-LEVEL WINDS ARE BECOMING MORE
FAVORABLE FOR ADDITIONAL DEVELOPMENT OVER THE NEXT COUPLE OF DAYS
AS THIS SYSTEM MOVES WEST-NORTHWESTWARD AROUND 10 MPH. THERE IS A
MEDIUM CHANCE...30 TO 50 PERCENT...OF THIS SYSTEM BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER BERG

Not looking too bad, center slowly but steadily consolidating and bands forming, and good outflow. Very large system.




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1418. Makoto1
That temperature is why you want to come up here for vacation, lol. 66, dew point 64. Rain let up just long enough to be able to grill, thankfully.
No surpise here.
000
ABNT20 KNHC 042333
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT SAT JUL 4 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE SHOWER ACTIVITY ASSOCIATED WITH A NON-TROPICAL AREA OF LOW
PRESSURE LOCATED ABOUT 800 MILES SOUTHWEST OF THE AZORES HAS BECOME
DISORGANIZED. UPPER-LEVEL WINDS ARE NOT FAVORABLE FOR DEVELOPMENT.
THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL OR SUBTROPICAL CYCLONE DURING THE NEXT 48
HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER AVILA
Looking awful.


Awaiting the EPAC TWO


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Quoting Tazmanian:
be come this dos not say any thing


Link


Different URL for Pacific vs Atlantic. Use this to be able to see both.
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Quoting btwntx08:
even hotter yet ughhh
Hearne, Texas (Airport)
Updated: 24 min 25 sec ago
119 °F
Scattered Clouds
Humidity: 36%
Dew Point: 85 °F
Wind: 10 mph from the SSE
Wind Gust: 17 mph
Pressure: 29.85 in (Steady)
Heat Index: 156 °F



Is that 156 F a typo???? But that is unbearable heat. You'd need one big AC!
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Quoting btwntx08:
even hotter yet ughhh
Hearne, Texas (Airport)
Updated: 24 min 25 sec ago
119 °F
Scattered Clouds
Humidity: 36%
Dew Point: 85 °F
Wind: 10 mph from the SSE
Wind Gust: 17 mph
Pressure: 29.85 in (Steady)
Heat Index: 156 °F



You may have found the location to the pits of hell, right there! Unbelieveable!
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yes its like one part is off too the W and the other part is closer too the MX coast line
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Slowly, but steadily organizing. Expect development chances upped by the NHC at the 8 PM TWO. Taz....what do you mean in terms of looking like 2 storms?... it's size?

Invest 94E Visible Loop
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Quoting Tazmanian:
i think 94E stans a better ch then 94L dos


Definitely. Much better environmental conditions for 94E than 94L. We do have to watch the wave approaching the Antilles, looks like it has a good rotation, and if it gets under some good conditions, may warrant some concern.
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hmmm 94E looks like two storms
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i think 94E stans a better ch then 94L dos
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be come this dos not say any thing


Link
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Finally some things in the tropics to track!
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94E doesn't look like any threat to land. Wont happen, but one of the models hooks it back towards California! Why doesn't the Wunderground main page have 94L up?
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now this is too funny


from the navy site


NOTE: The Atlantic wins the contest.
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Quoting KEEPEROFTHEGATE:


cen fix
15n/73w
Quoting extreme236:
lol gotta love the Navy NRL's humor:

NOTE: The Atlantic wins the contest...


Keeper - Any chance for development in your opinion? Some bloggers have said conditions are getting more favorable in the Caribbean

Extreme - Yeah, I have never seen this from NAVY/NRL before, but it is funny.
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000
WHXX01 KMIA 042002
CHGE77
TROPICAL CYCLONE GUIDANCE MESSAGE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2002 UTC SAT JUL 4 2009

DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.
PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE
AND SUBTROPICAL CYCLONE INFORMATION.

EAST PACIFIC OBJECTIVE AIDS FOR

DISTURBANCE INVEST (EP942009) 20090704 1800 UTC

...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...
090704 1800 090705 0600 090705 1800 090706 0600

LAT LON LAT LON LAT LON LAT LON
BAMS 14.6N 104.6W 15.8N 107.0W 16.8N 109.5W 17.7N 111.9W
BAMD 14.6N 104.6W 15.4N 107.1W 16.3N 109.5W 16.9N 111.7W
BAMM 14.6N 104.6W 15.7N 107.1W 16.6N 109.5W 17.3N 111.8W
LBAR 14.6N 104.6W 15.4N 107.2W 16.4N 110.1W 17.6N 113.0W
SHIP 25KTS 32KTS 40KTS 48KTS
DSHP 25KTS 32KTS 40KTS 48KTS

...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...
090706 1800 090707 1800 090708 1800 090709 1800

LAT LON LAT LON LAT LON LAT LON
BAMS 18.3N 114.2W 19.1N 118.2W 19.9N 121.2W 20.6N 123.7W
BAMD 17.6N 113.9W 18.7N 118.0W 20.3N 121.8W 21.9N 124.7W
BAMM 17.8N 114.1W 18.7N 118.2W 20.0N 121.4W 21.3N 124.0W
LBAR 18.6N 115.9W 20.9N 121.5W 24.3N 125.0W 29.7N 124.2W
SHIP 53KTS 54KTS 44KTS 38KTS
DSHP 53KTS 54KTS 44KTS 38KTS

...INITIAL CONDITIONS...
LATCUR = 14.6N LONCUR = 104.6W DIRCUR = 285DEG SPDCUR = 11KT
LATM12 = 14.2N LONM12 = 102.3W DIRM12 = 292DEG SPDM12 = 11KT
LATM24 = 13.0N LONM24 = 100.4W
WNDCUR = 25KT RMAXWD = 90NM WNDM12 = 25KT
CENPRS = 1009MB OUTPRS = 1011MB OUTRAD = 120NM SDEPTH = M
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM
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Quoting atmoaggie:
Can you imagine being stuck in traffic while it approaches? What fun.



Where was this pic taken and when?
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Invest 94E - After no invests for a few days, 2 in 1 day for Navy/NRL
--NHC will probably bump development chances up to medium at 8 pm.
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1399. bappit
That's believable with relative humidity of 17%.
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About JeffMasters

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.