Genesis of New Atlantic Tropical Cyclones: Which Model Should You Trust?

By: Dr. Jeff Masters , 3:29 PM GMT on August 29, 2013

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It's been a remarkably quiet late August in the Atlantic for hurricanes, with nary an "Invest", and precious few yellow 10% probability circles on NHC's Tropical Weather Outlook. When will this remarkable hurricane drought come to an end? The computer models we use to track hurricanes have conflicting ideas about this. Which model should we believe, and how far into the future can these models successfully predict genesis events of new tropical depressions in the Atlantic? Some answers come in a 2013 paper by a group of scientists led by Florida State's Daniel Halperin, just accepted for publication in the journal Weather and Forecasting, "An evaluation of tropical cyclone genesis forecasts from global numerical models." It turns out that two of the three most reliable models for predicting the genesis of tropical cyclones up to four days in advance are also the our top-performing models for predicting hurricane tracks: the American GFS model and the European ECMWF model. The UKMET model is also quite good at predicting tropical cyclone genesis events. The Canadian GEM model and the Navy NOGAPS model (now succeeded by the Navy NAVGEM model) do less well. When two or more models make the same genesis forecast, the odds of the event actually occurring are increased considerably. The models have improved greatly in making genesis forecasts in recent years; back in 2007, when our top three models made a 4-day genesis forecast, these verified only 17 - 28% of the time. By 2011, the hit rate had increased to 45 - 50%. However, the models still miss most genesis events. In 2011, the probability of detection of a tropical cyclone genesis event was only 8% - 23%, meaning that 77 - 92% of time, a tropical depression or tropical storm formed without the model predicting that it would form. The best model to use for looking at Atlantic tropical cyclone genesis in 2011 was the UKMET model, which combined a relatively high probability of detection rate with a low false alarm rate.


Figure 1. The probability of making a correct tropical cyclone genesis forecast for all forecast hours (06 to 96) by model, for the period 2004 - 2011. In 2011, three models--the GFS, UKMET, and European--made genesis forecasts that were correct 45 - 50% of the time. The Canadian GEM model and the Navy NOGAPS model did less well. Data taken from Halperin et al., 2013, "An evaluation of tropical cyclone genesis forecasts from global numerical models." Weather and Forecasting, doi: http://dx.doi.org/10.1175/WAF-D-13-00008.1

The paper looked at 135 Atlantic genesis events over the period 2004 - 2011, as predicted by five global computer weather forecast models: the GFS, ECMWF, UKMET, NOGAPS, and Canadian GEM. The regional GFDL and HWRF hurricane models were not considered, as they use output from the GFS model to drive them, and are not good at making genesis forecasts. The study only looked at forecasts made up to four days in advance. While there have been cases where I've seen genesis predictions made 7 - 10 days in advance come true, these are rare, and the "hit" rate of successful genesis forecasts even four days in advance is low. In the paper, a "hit" was defined as a forecast that successfully predicted genesis within 24 hours and 345 miles of the observed time and location. A "false alarm" occurred when the model predicted a storm that never developed. The other categories considered were "late genesis" events where a storm formed more than 24 hours before it was predicted to, and "early genesis", where a storm formed more than 24 hours after it was predicted to. Here are some details on each model's ability to make Atlantic tropical cyclone genesis forecasts:

European ECMWF model: The model is reluctant to predict genesis, and misses many genesis events (it had only an 8% probability of detection in 2011.) However, when it does predict genesis, it usually happens, with only a 16% false alarm percentage in 2011. The European model exhibits preferred regions of genesis, with over 60% of its genesis forecasts occurring in the MDR: 10-20°N, 60-20°W. Although the ECMWF misses many tropical cyclone genesis events in the Gulf of Mexico (as do the other models), when it does forecast genesis there, it almost always occurs. The model was highly prone to making late genesis forecasts.

American GFS model: The GFS model improved substantially in its genesis forecasts beginning in 2010, most likely due to a major model upgrade in 2010. The GFS is more aggressive at predicting genesis than the European model, and is less likely to miss a genesis event (22% probability of detection in 2011.) However, the incidence of false alarms was 32% in 2011, double what the European model had. Like the European model, the GFS exhibits preferred regions of genesis, with nearly 60% of its genesis forecasts occurring in the MDR: 10-20°N, 60-20°W.

UKMET model: The UKMET is more aggressive at predicting genesis than the European model, and is less likely to miss a genesis event (20% probability of detection in 2011.) The incidence of false alarms was 18% in 2011, similar to what the European model had. Like the European and GFS models, the UKMET exhibits preferred regions of genesis, with more than 67% of its genesis forecasts occurring in the MDR: 10-20°N, 60-20°W. The model was prone to making late genesis forecasts.

Canadian GEM model: The Canadian model was the least likely to miss a formation event, with a 23% probability of detection in 2011. False alarms have been a major issue, though, and the Canadian model generated the second highest number of bogus genesis events of any of the five models evaluated (42% of all its genesis forecasts in 2011 were false alarms.) The Canadian model does not seem to have a preferred region of genesis—all types of genesis events occur across the entire basin. The model performs best over the main development region (MDR; 10-20°N, 60-20°W), Caribbean Sea, and Gulf of Mexico (GOM).

Navy NOGAPS model: This model was retired in 2012, but we may be able to assume that its successor, the NAVGEM model, will have some of the same characteristics. False Alarms have been a major issue, and the NOGAPS model generated the highest number of bogus genesis events of any of the five models evaluated (60% of all its genesis forecasts in 2011 were false alarms.) The model also had a low probability of detection, just 9%. NOGAPS model does not seem to have a preferred region of genesis—all types of genesis events occur across the entire basin. Despite the high levels of hurricane activity in 2004 and 2005, the NOGAPS model failed to successfully forecast any genesis events those years.

Sources of Model Data
You can view 7-day ECMWF and 16-day GFS forecasts on wunderground's wundermap with the model layer turned on.
Longer ten-day ECMWF forecasts are available from the ECMWF web site.
FSU's experimental hurricane forecast page (CMC, ECMWF, GFDL, GFS, HWRF, and NAVGEM models)
NOAA's HFIP model comparison page (GFS, ECMWF, FIM, FIM9, UKMET, and CMC models.)
Experimental HFIP models

Very Quiet in the Atlantic
A tropical wave that came off the coast of Africa on Sunday is midway between Africa and the Lesser Antilles Islands. This disturbance is moving westward at 15 mph, has a modest amount of spin, but only a limited amount of heavy thunderstorm activity. In their 8 am EDT Thursday Tropical Weather Outlook, NHC left the 5-day odds of formation of this disturbance at 20%, but increased the 2-day odds of formation to 10%. Wind shear is a moderate 10 - 20 knots over the system, but there is an area of dry air and dust from the Saharan Air Layer (SAL) to the north and west that is interfering with development. With the exception of the NAVGEM model, there is little support from the models for developing the disturbance during the next five days. The wave could spread heavy rains and gusty winds to the Lesser Antilles Islands on Sunday and Monday.

A tropical wave expected to emerge from the coast of Africa on Friday and track over the Cape Verde Islands is also showing little support for development from the models. This wave is expected to take a northwesterly track, and would likely not be able to make the long trek across the Atlantic to threaten North America or the Caribbean Islands. In their 8 am EDT Thursday Tropical Weather Outlook, NHC put the 5-day odds of development at 20%.

Wunderblogger Lee Grenci has an excellent new post, "Atlantic Hurricane Season: The Saharan Air Layer and Vertical Wind Shear".

California's Rim Fire Now 6th Largest in State History, and is 30% Controlled
California's massive Rim Fire in Yosemite National Park continues to grow, but an army of over 4,000 firefighters are making headway against the blaze, and had attained 30% containment of the fire as of 9:20 am EDT on Thursday. According to Inciweb, fire has burned over 192,700 acres. This moves the fire into 6th place for largest fire in state history, according to statistics tabulated by wunderground's weather historian, Christopher C. Burt in his latest post, "The Worst Wild Fires in U.S. History". The Rim Fire will have difficultly surpassing California's largest fire on record--the Cedar Fire in San Diego County of October 2003. That fire burned 273,246 acres (430 square miles). California has had its driest year-to-date period, so it is no surprise that the state is experiencing an unusually large fire this summer.


Video 1. Time-lapse photography shows various perspectives of the 2013 Rim Fire, as viewed from Yosemite National Park. The first part of this video is from the Crane Flat Helibase. The fire is currently burning in wilderness and is not immediately threatening visitors or employees. The second half of the video is from Glacier Point, showing Yosemite Valley, and how little the smoke from the fire has impacted the Valley.

Jeff Masters

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Quoting 1127. GatorWX:


Englewood (Charlotte Countty side)


Westside! I miss those days. Link
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I see lots of wind shear out there
Member Since: March 12, 2013 Posts: 8 Comments: 12855
1132. GatorWX
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TROPICAL WEATHER OUTLOOK...CORRECTED
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT FRI AUG 30 2013

CORRECTED TO ADD...HIGH CHANCE...IN FIRST PARAGRAPH

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

THE BROAD AREA OF LOW PRESSURE ASSOCIATED WITH A TROPICAL WAVE HAS
SLOWED DOWN AND IT IS STILL LOCATED OVER EXTREME WESTERN AFRICA.
ENVIRONMENTAL CONDITIONS APPEAR CONDUCIVE FOR DEVELOPMENT...AND THIS
SYSTEM HAS THE POTENTIAL TO BECOME A TROPICAL DEPRESSION DURING THE
NEXT COUPLE OF DAYS WHEN THE LOW MOVES BETWEEN THE WEST COAST OF
AFRICA AND THE CAPE VERDE ISLANDS. AFTER THAT TIME...CONDITIONS ARE
EXPECTED TO BECOME A LESS CONDUCIVE FOR DEVELOPMENT AS THE
DISTURBANCE MOVES TOWARD THE WEST-NORTHWEST OVER THE EASTERN
ATLANTIC. THE SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING
A TROPICAL CYCLONE DURING THE NEXT 48 HOURS...AND A HIGH CHANCE...60
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 5 DAYS.
WHETHER THIS SYSTEM BECOMES A TROPICAL CYCLONE OR NOT...IT WILL
LIKELY BRING CLOUDINESS AND THUNDERSTORMS TO PORTIONS OF THE CAPE
VERDE ISLANDS IN THE NEXT 2 OR 3 DAYS.
Member Since: March 12, 2013 Posts: 8 Comments: 12855
1130. K8eCane
nothing. nada. zilch
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I know I'm just a novice. But I don't understand why so many categorize this season as a bust. Yes there have been no majors (yet). But there have been very interesting tropical systems to track and to learn from. Some, like Dorian the zombie storm, that wouldn't die, kept the blog guessing, and was at least to me pretty interesting. I think the activity and unusual flow off the East coast of US has also been interesting. Isn't this what meteorology is really about? We still have till Nov. and as I said, I think this season is a "late-bloomer, and we still will see some "real" action before all is said and done.
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The MJO that couldn't really ever make into the Caribbean.

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1127. GatorWX
Quoting 1118. FtMyersgal:


Where is "here" ?


Englewood (Charlotte Countty side)
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1125. Grothar
Joe Bastardi's forecast for 2013

Link
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1124. GatorWX
Quoting 1101. Sfloridacat5:
About 8-9 pm last night picked up 1.14" of unexpected rain at our house in Ft. Myers (just east of I75)


Nice wave, btw. I was in NY State during that one. I remember Dennis, Ivan, Katrina and Rita well though. Neat when the surf goes off here, since it rarely does. It was funny seeing so many east coasters over here during those Gulf storms. Ivan had the best swell here in Englewood IMO. Swell rolled over the beach pilings, which was the only time I've seen that happen. It was a couple feet overhead here and very clean, but almost double overhead at North Jetty, Venice. Really nice clean swell.
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Yeah I think after 3 active season in a row that this year may be more in line with what we had in 2009. Sorry folks that means many blog meltdown days ahead.
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Quoting 1116. StormTrackerScott:
Very unusual.



The satellite picture of the GOM looks like it's December.
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I just hope this nice weather pattern continues at least until Monday here on the Mississippi Alabama Gulf Coast.
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This season tells me that nature - and not models - is in control of this 'hurricane season'.
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Quoting 1094. GatorWX:



This is most interesting to me. Has been stationary here for many days. When is shear due to lessen in this area? If shear lessened I think this might develop. It is very tenacious.
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Quoting 1115. GatorWX:


I picked up close to 2/3" around 6:30pm. 9 days in a row over .5". We have to be close to 30-35", at least here, since late May, perhaps more. This is the wettest summer I ever remember, been here my whole life.


Where is "here" ?
Member Since: September 16, 2010 Posts: 0 Comments: 1216
THIS SEASON IS A YAWN!
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Very unusual.

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1115. GatorWX
Quoting 1101. Sfloridacat5:
About 8-9 pm last night picked up 1.14" of unexpected rain at our house in Ft. Myers (just east of I75)


I picked up close to 2/3" around 6:30pm. 9 days in a row over .5". We have to be close to 30-35", at least here, since late May, perhaps more. This is the wettest summer I ever remember, been here my whole life.
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Good day all...

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And next year there will be downcasting predictions, then it will be like 2004!
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Quoting 1108. IKE:

2m
Incredible lack of tropical
activity GLOBALLY probably due in at least part to drying mid/upper
levels, OPPOSITE OF IPCC AND EPA contentions..........
Bastardi again, huh? Speaking of "one of those people"... ;-)
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The moral of this tropical story this year is if someone tells you in June what the season is going to be like in September, believe them.
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1110. SLU
Quoting 1086. IKE:
Yawn.....to the ATL. Will there be a hurricane in the region in 2013? Will not happen in August and may not for at least the first few days of September.

It peaks my curiosity just to see when and IF it will happen. Incredible to watch.


Forget a hurricane, we can't even get a half decent looking tropical wave to watch. Isn't the MJO already in phase 1? I'm totally flummoxed with 2013.

Member Since: July 13, 2006 Posts: 12 Comments: 4799
From Miami NWS Disco

LONG TERM...

THERE IS ALSO A TROPICAL WAVE OVER THE CENTRAL ATLANTIC WATERS
THAT IS FORECAST BY THE MODELS TO MOVE WEST-NORTHWEST NEXT WEEK
AND POSSIBILITY OVER SOUTH FLORIDA BY END OF NEXT WEEK. IF THIS
TREND CONDITIONS THEN THE POPS MAY HAVE TO BE RAISED UP FOR NEXT OF
NEXT WEEK.
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1108. IKE

2m
Incredible lack of tropical
activity GLOBALLY probably due in at least part to drying mid/upper
levels, OPPOSITE OF IPCC AND EPA contentions..........
...................................... ...
Think I'll go mow my front yard. More spinning in that then what's in the ATL.Number of hurricanes in the ATL this season....0.Number of 70 mph TS's in the ATL this season....0.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting 1104. chipsf64:
Invest 96L over land really that's is a first. You guys are really getting desperate now .. Dag gone .. Actually only had 1 storm this year . C,D,E storms formed where there were no buoy's . You are naming clouds . If hurricane hunters flew into B,F storms that was a total waste of tax dollars . 4 C130 turbo prop engines get great fuel mileage..
Oh, you're one of those people. Got it. (Turns and quickly runs to opposite end of the room.)
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Quoting 1103. Neapolitan:
Quota? What quota? I've not heard of any quota. Who sets it? How many tropical cyclones are needed to fill it? Tell us, please; inquiring minds want to know!
NHPC 18-23 then they change it mid season . I am sorry if I happen to be taking my frustrations of the weather channel out on you but was very disappointed when then bought you. I have been a member since 2003 You are the best I love your interviews with Amy Goodman . Watch the weather channel and you will see my point
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BORING GFS, only weak fishes....
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Invest 96L over land really that's is a first. You guys are really getting desperate now .. Dag gone .. Actually only had 1 storm this year . C,D,E storms formed where there were no buoy's . You are naming clouds . If hurricane hunters flew into B,F storms that was a total waste of tax dollars . 4 C130 turbo prop engines get great fuel mileage..
Member Since: Posts: Comments:
Quoting 1100. chipsf64:
I agree.. they love the crystal ball.. at this point if they could make hurricanes they would just to meet their quota
Quota? What quota? I've not heard of any quota. Who sets it? How many tropical cyclones are needed to fill it? Tell us, please; inquiring minds want to know!
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Quoting 1101. Sfloridacat5:
About 8-9 pm last night picked up 1.14" of unexpected rain at our house in Ft. Myers (just east of I75)


I'm east of I75 also. Got .73" and the radar wasn't showing any storms. Strange.
Member Since: September 16, 2010 Posts: 0 Comments: 1216
About 8-9 pm last night picked up 1.14" of unexpected rain at our house in Ft. Myers (just east of I75)
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Quoting 1079. CaneHunter031472:


I'll have the cheese and Chorizo Quesadillas please. Apple Juice.

thank you
I agree.. they love the crystal ball.. at this point if they could make hurricanes they would just to meet their quota
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1099. GatorWX
Quoting 1064. barbamz:
Good morning from sunny Germany. Heads up once again in mid and western Mediterranean today:


Saved image. Source


Cloud top temperatures.

Alert level 2 from Estofex (European Storm Forecast Experiment).

Have a nice day everyone!





I hope all that crazy weather in Europe lets up before mid-September! Not sure how bad it's been recently however.
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1098. Kyon5
Shear is about 30 kts just north of the wave. We'll see what happens.



* This is a shear map, it just shows what the tendency has been like the past 24 hours. On the right corner, you can see the legend indicating the current wind shear.
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Stormy day today across most of FL. Flooding & lightning seem to be the main issues later today.

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL FLORIDA.

.DAY ONE...TODAY AND TONIGHT.

.THUNDERSTORM IMPACT...
A COLD FRONT APPROACHING THE FLORIDA GEORGIA BORDER LATER TODAY...
AN UPPER LOW ACROSS SOUTH FLORIDA...AND THE DEVELOPING EAST COAST
SEA BREEZE THIS AFTERNOON WILL LEAD TO SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS EAST CENTRAL FLORIDA. STORMS ARE EXPECTED TO
DEVELOP ACROSS THE NORTHERN FLORIDA PENINSULA INCLUDING NORTHERN
LAKE AND VOLUSIA COUNTIES BY MID AFTERNOON WITH OTHER SCATTERED
LIGHTNING STORMS FORMING ALONG THE EAST COAST SEA BREEZE ALONG THE
TREASURE COAST WHICH WILL DEVELOP AND PROPAGATE SLOWLY INLAND WITH
THUNDERSTORM OUTFLOW BOUNDARIES. THE MAIN THUNDERSTORM HAZARDS
WILL BE FREQUENT CLOUD TO GROUND LIGHTNING STRIKES...GUSTY WINDS
TO 45 MPH AND HEAVY RAINFALL.

.FLOOD IMPACT...
LOCALLY HEAVY RAINFALL AMOUNTS OF TWO TO THREE INCHES WILL BE
POSSIBLE WITH STRONGER SLOW MOVING STORMS THIS AFTERNOON. HEAVY
RAIN MAY CAUSE FLOODING OF POOR DRAINAGE AREAS.


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1096. Kyon5


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1095. MahFL
Could be a new coc trying to form.

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1094. GatorWX
Quoting 1084. SFLWeatherman:



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1093. txjac
LOL ...wow, everyone has new avitars this morning!
Love it
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1092. beell
Based on some of the Global Hawk data, the central Atlantic wave is probably under about 30 knots of westerly shear. Possibly increasing for today.



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Now that the dry air is gone SHEAR comes into the game..-_-.This season is really incredible isn't it..
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1090. GatorWX
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1089. GatorWX
Quoting 1086. IKE:
Yawn.....to the ATL. Will there be a hurricane in the region in 2013? Will not happen in August and may not for at least the first few days of September.

It peaks my curiosity just to see when and IF it will happen. Incredible to watch.


Take a look at the xtrp model, I hear it goes out indefinitely.
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1088. GatorWX
Go to bed with the distant sound of thunder from storms offshore, wake up to the same. Love it. Now stay there, I want to go out to the beach or take the kayak out! No yard work or any work for me today. Shall be a day of leisure!!



74 F, 98% RH, 74 F DP (:P), 40% Chance of Precip. Kinda sticky for 0730, but it ain't hot yet. 91 F forecasted high.
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florida ull? john hope said they can spin spin and spin. if the ull moves slightly sw and something actually develops fl.could be in for it.
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1086. IKE
Yawn.....to the ATL. Will there be a hurricane in the region in 2013? Will not happen in August and may not for at least the first few days of September.

It peaks my curiosity just to see when and IF it will happen. Incredible to watch.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1085. IKE
TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT FRI AUG 30 2013

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

THE BROAD AREA OF LOW PRESSURE ASSOCIATED WITH A TROPICAL WAVE HAS
SLOWED DOWN
AND IT IS STILL LOCATED OVER EXTREME WESTERN AFRICA.
ENVIRONMENTAL CONDITIONS APPEAR CONDUCIVE FOR DEVELOPMENT...AND THIS
SYSTEM HAS THE POTENTIAL TO BECOME A TROPICAL DEPRESSION DURING THE
NEXT COUPLE OF DAYS WHEN THE LOW MOVES BETWEEN THE WEST COAST OF
AFRICA AND THE CAPE VERDE ISLANDS. AFTER THAT TIME...CONDITIONS ARE
EXPECTED TO BECOME A LESS CONDUCIVE FOR DEVELOPMENT AS THE
DISTURBANCE MOVES TOWARD THE WEST-NORTHWEST OVER THE EASTERN
ATLANTIC.
THE SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING
A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AND...60 PERCENT OF
BECOMING A TROPICAL CYCLONE DURING THE NEXT 5 DAYS. WHETHER THIS
SYSTEM BECOMES A TROPICAL CYCLONE OR NOT...IT WILL LIKELY BRING
CLOUDINESS AND THUNDERSTORMS TO PORTIONS OF THE CAPE VERDE ISLANDS
IN THE NEXT 2 OR 3 DAYS.

SHOWER ACTIVITY ASSOCIATED WITH A TROPICAL WAVE LOCATED ABOUT 700
MILES EAST OF THE LESSER ANTILLES REMAINS DISORGANIZED. THIS
DISTURBANCE IS EXPECTED TO MOVE WESTWARD TOWARD A REGION WHERE THE
UPPER-LEVEL WINDS ARE NOT FAVORABLE FOR DEVELOPMENT
. THIS SYSTEM
HAS A LOW CHANCE...10 PERCENT...OF BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS...AND A LOW CHANCE...20 PERCENT...OF
BECOMING A TROPICAL CYCLONE DURING THE NEXT 5 DAYS.

&&

FIVE-DAY FORMATION PROBABILITIES ARE EXPERIMENTAL IN 2013. COMMENTS
ON THE EXPERIMENTAL FORECASTS CAN BE PROVIDED AT...

WWW.NWS.NOAA.GOV/SURVEY/NWS-SURVEY.PHP?CODE=ETWO

$$
FORECASTER AVILA
Member Since: June 9, 2005 Posts: 23 Comments: 37858

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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.