Isaac slamming Gulf Coast with damaging floods, tornadoes

By: Dr. Jeff Masters , 4:44 PM GMT on August 30, 2012

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Slow-moving Tropical Storm Isaac continues to hammer coastal Louisiana, Mississippi, Alabama, and Florida's Panhandle with tornadoes, torrential rains, high winds, and a damaging storm surge. Over the past 24 hours, destructive tornadoes have touched down in Biloxi and Pascagoula, Mississippi, and one person was killed by a tree falling on a car in Pearl River County, Mississippi. A major flood event is occurring in Slidell, Louisiana, where Isaac's storm surge filled Bayou Bonfouca and the W-14 Canal, inundating portions of the city with 1 - 5 feet of water. While Isaac is now a weakening minimal-strength tropical storm, it is still a potent rainmaker, and will cause damaging floods all along its path for the next three days. Major river flooding is occurring or is about to occur on a number of rivers in the landfall area. In north central Tangipahoa Parish in southeast Louisiana and southwestern Pike County in southern Mississippi, a mandatory evacuation has been ordered for all low-lying areas and along the Tangipahoa River, due to the potential failure of the Lake Tangipahoa dam. Audubon Park in New Orleans, recorded 11.19" of rain as of 7 pm Wednesday night. An earlier amount of 19" was found to be erroneous, and this is not a 24-hour precipitation record for the city. According to wunderground's weather historian, Christopher C. Burt, New Orleans' greatest 24-hour rainfall on record is 14.01" on July 24 - 25, 1933. The Louisiana official state 24-hour record is 22.00" on Aug. 29, 1962 at Hakberry, although U.S. Army Corps of Engineers `Storm Studies' mentions a 23.80" falling in a 24-hour period at Millers Island during a TS on Aug 7-8, 1940. Storm total was 37.50" over a 60-hour period there during that event.

A few other rainfall totals from Isaac, through 11 am EDT on Thursday:

15.02" Marion, MS
10.09" Hattiesburg, MS
10.15" Gulfport, MS
9.80" Slidell, LA
9.74" Biloxi, MS
8.52" Mobile, AL
5.57" Baton Rouge, LA


Figure 1. Isaac's winds and storm surge overcomes the seawall and floods South Beach Boulevard in Waveland, Miss., Wednesday, Aug. 29, 2012, the seventh anniversary of Hurricane Katrina hitting the Gulf Coast. (AP Photo/Rogelio V. Solis). Waveland experienced a storm surge in excess of 5' for 36 hours.

Isaac's storm surge winds down
Storm surge levels along the coast of Mississippi and surrounding areas are gradually receding, and the surge has finally fallen below 5' at Waveland, which experienced a storm surge in excess of 5' for 36 hours. Isaac's storm surge levels were characteristic of a Category 2 hurricane, and lasted for an exceptionally long period of time. Waveland, Mississippi experienced a peak surge of 8' and peak storm tide of 9' (surge plus the natural high tide), which beat the levels that occurred during Category 2 Hurricane Gustav of 2008 (7' of storm tide.) The peak 11.06' storm surge at Shell Beach, which is in Lake Borgne, 30 miles southeast of New Orleans, exceeded the 9.5' surge recorded there during Gustav. According to an article in nola.com, Isaac pushed a storm surge of 13.6' into Lake Borgne, on the east side of New Orleans. This is not far from the 15.5' storm surge Hurricane Katrina brought to the location. It is quite possible that Isaac's storm surge might have breached levees of the east side of New Orleans, flooding areas inhabited by tens of thousands of people, had the Army Corps of Engineers not completed their $14.5 billion upgrade to the New Orleans flood defenses this year. I estimate that storm surge damage from Isaac will exceed $2 billion. Isaac has likely caused $2.5 billion in insured damage not related to flooding, insurance firm Eqecat estimated yesterday. Here were some of the peak storm surge values that were recorded at NOAA tide gauges during Isaac:

11.1' Shell Beach, LA
8.0' Waveland, MS
3.5' Pensacola, FL
4.6' Pascagoula, MS
3.8' Mobile, AL


Figure 2. A TRMM satellite 3-D view of rainfall on Aug. 28 showed a few very powerful thunderstorms near Isaac's eye were reaching heights of almost 17 km (10.6 miles.) Intense bands of rain around Isaac were occasionally dropping rain at a rate of over 2.75 inches per hour. Image credit: SSAI/NASA, Hal Pierce.

Isaac's storm surge on the Mississippi River
A storm surge estimated at 12' moved up the Mississippi in Plaquemines Parish near Port Sulphur, LA, near 8:30 pm EDT Tuesday, causing overtopping of the levees and flooding of homes in the mandatory evacuation areas behind the levees. These levees were not part of the $14.5 billion levee upgrade New Orleans got after Hurricane Katrina, and were not rated to Category 3 hurricane strength, like the levees protecting New Orleans are. Since salt water is more dense than fresh water, the surge travelled along the bottom of the river, with the fresh water flow of the river lying on top. The surge continued upriver, and before reaching New Orleans, encountered an underwater barrier in Plaquemines Parish. This barrier was constructed by the Army Corps of Engineers beginning on August 15, in order to keep salt water from moving upstream and contaminating drinking water for Plaquemines Parish and New Orleans. Salt water had made it 90 miles upriver to the outskirts of New Orleans, due to the low flow rate of the river (which had dropped 7' below average in height due to the drought of 2012.) According to a spokesperson for the National Weather Service River Forecast Office, this barrier was probably able to completely block the flow of salt water upriver due to Isaac's storm surge, and no salt water made it as far as New Orleans. However, the massive intrusion of ocean water into the river channel caused the mighty Mississippi's fresh water flow to back up for hundreds of miles. Water levels were elevated by 10' in New Orleans (103 miles upstream from the mouth of the Mississippi), 8' in Baton Rouge (228 miles upstream), and 1.4' at Knox Landing, an amazing 314 miles upstream.

Hurricane Kirk in the Central Atlantic
Hurricane Kirk intensified into a 75 mph Category 1 hurricane this morning, becoming the busy 2012 Atlantic hurricane season's fifth hurricane. With the season's mid-point of September 10 still almost 2 weeks away, we've already had 12 named storms and 5 hurricanes, which is close to what an entire season experiences in an average year (11 named storms and 6 hurricanes.) Kirk should stay well out to sea and not trouble any land areas.


Figure 3. Morning satellite image of Hurricane Kirk.

Tropical Storm Leslie forms in the Central Atlantic
Tropical Storm Leslie has formed in the Central Atlantic. Leslie's formation on August 30 puts 2012 in 2nd place for earliest formation date of the season's 12th storm. Only 1995 had an earlier formation date of the season's 12th storm. With records dating back to 1851, this year is only the second time 8 total storms have formed in August. The other year was 2004, when the first storm of the season formed on August 1 (Alex), and the 8th storm (Hermine)
formed on August 29th. Leslie is organizing quickly, and appears destined to become a hurricane before the week is out. Fortunately, Hurricane Kirk is weakening the ridge of high pressure to the north of Leslie, and Leslie is expected to turn to the northwest and miss the Lesser Antilles Islands. In the long term, it remains unclear if Leslie will follow Kirk and fully recurve out to sea. The latest 2 runs of the GFS model have predicted that Leslie will recurve out to sea and not threaten any land areas, but the latest 2 runs of the ECMWF model have predicted that the trough of low pressure pulling Kirk to the northeast will not be strong enough to recurve Leslie out to sea. Instead, the ECMWF predicts that a ridge of high pressure will build in early next week, forcing Leslie more to the northwest, making the storm a potential threat to Bermuda, then to the Northeast U.S. and Canada in 8 - 11 days.

Jeff Masters

Hurricane Isaac Louisiana (apphotos)
Two men walk in the storm surge from Isaac, on Lakeshore Drive along Lake Pontchartrain, as the storm approaches landfall, in New Orleans, Tuesday, Aug. 28, 2012. (AP Photo/Gerald Herbert)
Hurricane Isaac Louisiana
west palm beach flood isaac (alishu)
West Palm Beach flood from Isaac
west palm beach flood isaac
Hurricane Isaac Impacts Navarre Beach & Pier10 (jennjeff1)
Hurricane Isaac versus Navarre Beach Pier, the longest concrete pier on the Gulf of Mexico
Hurricane Isaac Impacts Navarre Beach & Pier10

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1438. LargoFl
BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE LITTLE ROCK AR
851 AM CDT FRI AUG 31 2012

THE NATIONAL WEATHER SERVICE IN LITTLE ROCK HAS ISSUED A

* FLASH FLOOD WARNING FOR...
CALHOUN COUNTY IN SOUTHWEST ARKANSAS...
EASTERN OUACHITA COUNTY IN SOUTHWEST ARKANSAS...
NORTHWESTERN BRADLEY COUNTY IN SOUTHEAST ARKANSAS...
SOUTHEASTERN DALLAS COUNTY IN SOUTHWEST ARKANSAS...
SOUTHERN CLEVELAND COUNTY IN SOUTHEAST ARKANSAS...

* UNTIL NOON CDT

* AT 849 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED AN
AREA OF THUNDERSTORMS WITH VERY HEAVY RAINFALL ALONG A LINE
EXTENDING FROM NEAR CRANE LAKE TO 2 MILES EAST OF CALION. DOPPLER
RADAR INDICATES 1 TO 2 INCHES OF RAIN HAVE FALLEN OVER PARTS OF THE
WARNED AREA IN THE PAST 2 HOURS. THIS IS IN ADDITION TO THE 2 TO 4
INCHES SEEN ON THURSDAY. WITH ADDITIONAL HEAVY RAIN EXPECTED...
FLASH FLOODING IS LIKELY TO OCCUR. WHILE PRECIPITATION MAY TAPER
OFF IN SOME AREAS DURING THE WARNING PERIOD...IT WILL TAKE SOME
TIME FOR ANY HIGH WATER TO RUNOFF.

* SOME LOCATIONS THAT WILL EXPERIENCE FLOODING INCLUDE...
HAMPTON... FORDYCE... WEEKS...
TRI COUNTY LAKE... TIPTON... THORNTON...
MILLERS BLUFF... LANARK... HEBRON...
HARRELL... HARLOW... HAMPTON MUNI ARPT...
GRAPEVINE LAKE... ELLISVILLE... CRANE LAKE...
BEARDEN... WOODBERRY... TINSMAN...

PRECAUTIONARY/PREPAREDNESS ACTIONS...

DO NOT UNDERESTIMATE THE POWER OF FLOOD WATERS. ONLY A FEW INCHES OF
RAPIDLY FLOWING WATER CAN QUICKLY CARRY AWAY YOUR VEHICLE. TURN
AROUND... DONT DROWN!

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1437. LargoFl
..shear model
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1436. LargoFl
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1435. LargoFl
Quoting NOLALawyer:
Power back on in Mandeville. Like many here predicted, including me, Isaac caught many people off guard and was much more than "just a Cat-1." Flooding from Madisonville came less than a 1/4 mile from my house and the town, and many others, are still submerged.

Quite an event.
glad you got power back and came thru this ok
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1434. Skyepony (Mod)
Quoting Jedkins01:


Well radar around here in Central Florida always highly underestimates, especially when it's a small region of rain, if the radar thinks that spot in Orland had 3 inches they probably had over 4 in reality. The only time it's closer to actual totals is when they switch to tropical Z/R.


Even with 5" of rain in 3hrs you wouldn't expect that amount of flooding. Here's a PWS in that area had 2.54". Everything else around there had less than 1/2 an inch.
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1433. LargoFl
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Power back on in Mandeville. Like many here predicted, including me, Isaac caught many people off guard and was much more than "just a Cat-1." Flooding from Madisonville came less than a 1/4 mile from my house and the town, and many others, are still submerged.

Quite an event.
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1431. VR46L
Quoting islander101010:
spin.noted.just.w.of.belice


You have a point there maybe worth keeping an eye on





Link
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1430. OcnGypZ
Quoting lobdelse81:

This would be bad news for Providence and the Narragansett Bay area. We all know what the Great New England Hurricane of 1938 did there.


PVD here. At least we have our hurricane barrier now, but that doesn't preclude damage to low lying areas along the Bay and Southcoast.
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1429. LargoFl
yet another one coming off africa
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1428. LargoFl
Quoting Brock31:
Fingers crossed for Leslie stalling like some of the forecasts are showing. Its been a while since I've seen a setup like this.
yeah in the current economic hard times the US doesnt need land falling hurricanes right now, just doesnt stop..bad news after bad news..pat was kidding about..the Mayan doom..hmmm
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1427. Brock31
Fingers crossed for Leslie stalling like some of the forecasts are showing. Its been a while since I've seen a setup like this.
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1426. MTWX
Update from SAR Team Yankee 1/ Portlight:

After being contacted by John Hosey, the VOAD coordinator for the Harrison County EOC Thursday morning, Jason and Bobby of Yankee 1 tarped 3 roofs, 1 in Gulf Port (elderly couple) and 2 in Biloxi (stroke victim and a pregnant lady) Meanwhile, back in the shelter at East Central High School in Jackson County, Doc Chandler and Cross had to deal with an inflow of evacuees from the areas that began rapidly flooding today. many of these evacuees showed up with almost nothing, Being rescued by the national guard from flooded homes. Some had to be given booties to wear not even having shoes.

Besides providing medical care, Yankee 1 also distributed hygiene kits provided by the American Red Cross and worked with shelter staff to meet the needs of the evacuees' sanitary and health needs.

Yankee 1 already has requests for relief work for Friday, 8/31, in Pass Christian (Harrison county). With the flooding, it is unlikely that Yankee 1 will be able to en...d the aid station mission before Sunday morning. There are so many evacuees, many with significant health problems, that the team cannot pull out and move elsewhere. If the flood waters recede in time we may have work around here, as this county got hammered in the floods. There are whole neighborhoods under water and apparently there is going to be even more if flood gates opened, according to what some evacuees are saying. Shelter staff and local officials are saying areas that did not flood during Katrina are now under water. Even though Isaac barely reached category 1 hurricane strength, it looks like Isaac may be on track to go down as another I storm like Ivan, Isabelle and Ike.

Special thanks to Portlight Strategies, Inc for springing for the tarps, nails and 1"x2" x8' slats we used to do emergency home repairs. Likewise a special shout-out to John Hosey the VOAD coordinator for Harrison Co. This disaster is far from over, and we encourage those who can give to do so. With the major media again focused on New Orleans the Mississippi Gulf Coast is once again in danger of becoming the forgotten coast. Although Yankee 1's primary mission is search and rescue, our calling and charter is focused on meeting the needs of resource-strapped communities affected by disasters, we are doing that here, please help us help them!
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1425. LargoFl
..check out saturday..in the right hand side of this pic
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Quoting ncstorm:
7.9 Earthquake in the Phillipines




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1423. LargoFl
Quoting watercayman:
Wow, 06Z GFS paints a pretty nervous week for Bermuda with that thing (Leslie) sitting directly below them, hovering, picking up strength.
yes something to watch next week for sure
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Quoting islander101010:
spin.noted.just.w.of.belice
West of Belize or East ?
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Quoting stormpetrol:


Looks like Leslie should pass north of Islands according to this.


Agree. When looking at the Atlantic water vapor, you can see this setting up and the jet stream moving south to pic up Leslie.
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Wow, 06Z GFS paints a pretty nervous week for Bermuda with that thing (Leslie) sitting directly below them, hovering, picking up strength.
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1419. LargoFl
this is only a rainfall model
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1418. LargoFl
Quoting weathermanwannabe:
Good Morning. One thing I've learned over the years on here, and particularly this season, is that the models will change on long-term basis as to any given storm a week out from potential from landfall; thus, trying to predict a potential landfall area a week or more out is pretty much useless.

In terms of threats to CONUS/Caribbean, we also know that NHC 5-Day forecasts are getting better, and, the 3-Day tracks have a pretty high degree of accuracy (in the general landfall ball park within a few hundred miles). Why?...........Because of the collateral information fed into the models from planes and other sources as to the large scale synoptic factors that will influence final approach steering. This boils down to upper air ridging features (strength or weaknesses that that the planes/balloons can detect) and the exact timing/speed of trofs which can erode the ridges.

Way too early to know with any certainty where a storm in the Central Atlantic might end up except for general guidance from the long-term models.
yes your right, way too early, lets see how they go say next thursday and where she is then
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Looks like Leslie should pass north of Islands according to this.
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Good Morning. One thing I've learned over the years on here, and particularly this season, is that the models will change on long-term basis as to any given storm a week out from potential from landfall; thus, trying to predict a potential landfall area a week or more out is pretty much useless.

In terms of threats to CONUS/Caribbean, we also know that NHC 5-Day forecasts are getting better, and, the 3-Day tracks have a pretty high degree of accuracy (in the general landfall ball park within a few hundred miles). Why?...........Because of the collateral information fed into the models from planes and other sources as to the large scale synoptic factors that will influence final approach steering. This boils down to upper air ridging features (strength or weaknesses that that the planes/balloons can detect) and the exact timing/speed of trofs which can erode the ridges.

Way too early to know with any certainty where a storm in the Central Atlantic might end up except for general guidance from the long-term models.
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More to watch, busy time of year.

Quoting islander101010:
spin.noted.just.w.of.belice

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spin.noted.just.w.of.belice
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1412. Dsntslp
Quoting LargoFl:
Almost looks like a hand reaching down and pinching and opening a screen on a touch phone.
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1411. LargoFl
...notice how next thursday how it stalls there, almost changed to due west that last frame huh
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1410. LargoFl
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1409. LargoFl
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1408. LargoFl
Quoting lobdelse81:

This would be bad news for Providence and the Narragansett Bay area. We all know what the Great New England Hurricane of 1938 did there.
these models can and do change often with their tracks but..this one we need to watch closely this coming week, next weekend could be..dangerous
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Way to far out to be even speculating about a landfall, worry about that if Leslie changes her mind when she's stalled out north of the islands.
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1406. LargoFl
Quoting Tazmanian:
None of this takes it out too sea any more


..gfs has it in..the northeast whew..hope this changes in a few days
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Quoting Waltanater:
You should also take a "Spelling" class.


don't incite rebellion amongst young WU members please
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Quoting LargoFl:
GFS at 240 hours..didnt some guy ask about a hurricane in NYC? just a few days ago?

This would be bad news for Providence and the Narragansett Bay area. We all know what the Great New England Hurricane of 1938 did there.
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1403. LargoFl
I do hope this changes..GFS at 252 hours...
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Quoting Skyepony:


Looks like some Isaac outflow & afternoon showers. One little spot had 3". I have to wonder if some drainage wasn't blocked..


Well radar around here in Central Florida always highly underestimates, especially when it's a small region of rain, if the radar thinks that spot in Orland had 3 inches they probably had over 4 in reality. The only time it's closer to actual totals is when they switch to tropical Z/R.
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Quoting CybrTeddy:
The general idea between the models this AM is that Leslie will begin to recurve north of the islands but stall out and weaken some at around 102 hours due to increasing shear, then will begin to bend back west slowly before being recurved into Canada. That's the thinking of the GFS/ECMWF at least.



For the time being. But the ecw and gfs will likey change 100 times for for all set and done
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1400. LargoFl
GFS at 240 hours..didnt some guy ask about a hurricane in NYC? just a few days ago?
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The models have definitely swung a little more west than yesterday afternoon and the GFS ensemble models have definitely increased the threat to the Northern East Coast somewhat... still gotta see if Leslie is going to stall or if there will be enough to push her out to sea. If she stalls, that could mean bad news down the road.

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The general idea between the models this AM is that Leslie will begin to recurve north of the islands but stall out and weaken some at around 102 hours due to increasing shear, then will begin to bend back west slowly before being recurved into Canada. That's the thinking of the GFS/ECMWF at least.
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1397. LargoFl
Quoting LargoFl:
folks..be careful..this is NOT issac..came from the african way......GFS at 228 hours
has a hurricane ever..hit washington d.c head on?
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Quoting ncstorm:
7.9 Earthquake in the Phillipines
Tsunami warning in effect.
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1395. LargoFl
here it is..GFS at 183 hours?..could this be Leslie after the stall?
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Quoting Tazmanian:
Not of this takes it out too sea any more



This looks similar to what happened with Hurricane Felix of 1995. It was a classic Cape Verde type storm which looked like it would recurve at one point but then I guess a high built in and then pushed him back west very close to North Carolina. Anyone think that this could be a good analogue for Leslie?
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Quoting FOREX:


Looks like Leslie went well South of her forecast point. Time to feed the models the correct information so we don't have another Isaac situation. Am I way off base??


ive been seeing the wnw turn in the last movies

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Quoting wxmobilejim:
I'm taking a tropical forecasting class at Penn State and my professor for this class is none other than Stacy Stewart from the NHC. He has given us great insite into how they predict expected rainfall total from tropical cyclones.
You should also take a "Spelling" class.
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1388. LargoFl
folks..be careful..this is NOT issac..came from the african way......GFS at 228 hours
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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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