Caribbean-On-Line's Caribbean Hurricane Blog



TROPICAL STORM HANNA DISCUSSION NUMBER 23

Published on September 2, 2008 12:46 PM | Comments

So Hanna was affected by shear and is blown apart a bit. The NHC discussion doesn't sound too confident of whether it will actually get back to hurricane strength or not but it is possible. Either way it is dumping a ton of rain on the area and still needs to be watched closely.

TROPICAL STORM HANNA DISCUSSION NUMBER 23 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082008 1100 AM EDT TUE SEP 02 2008

HANNA HAS FINALLY SUCCUMBED TO THE STRONG VERTICAL SHEAR WITH VISIBLE SATELLITE IMAGERY SHOWING A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION AND A SHRINKING CDO FEATURE. THE INITIAL INTENSITY IS SET AT 60 KT...BUT GIVEN THE CURRENT SATELLITE PRESENTATION...THIS MIGHT BE A BIT GENEROUS. AN AIR FORCE RECONNAISSANCE AIRCRAFT WILL INVESTIGATE HANNA THIS AFTERNOON AND PROVIDE A BETTER INTENSITY ESTIMATE. WATER VAPOR IMAGERY SHOWS A SHARP EDGE OR DEFORMATION AXIS ON THE NORTH SIDE OF THE CIRRUS CANOPY SUGGESTING THAT THE SHEAR WILL PERSIST IN THE SHORT-TERM...AND SOME ADDITIONAL WEAKENING IS POSSIBLE TODAY AND TONIGHT. IN ABOUT 24 HOURS...GLOBAL MODELS SHOW THE SHEAR WEAKENING AND THIS COULD ALLOW HANNA TO RESTRENGTHEN. HOWEVER...GIVEN THE PRESENT LACK OF ORGANIZATION...IT IS DIFFICULT TO KNOW HOW MUCH STRENGTHENING IS POSSIBLE. THE NEW OFFICIAL FORECAST IS LOWER THAN THE PREVIOUS ADVISORY BUT SHOWS HANNA BECOMING A CATEGORY ONE HURRICANE IN ABOUT 36 HOURS. IT SHOULD BE NOTED THAT THIS IS A LOW CONFIDENCE FORECAST. IN FACT...IF ONE CONSULTS THE WIND SPEED PROBABILITY PRODUCT INCLUDED IN THIS PACKAGE...IT CAN BE SEEN THAT THERE IS NEARLY AN EQUAL PROBABILITY OF HANNA BEING A TROPICAL STORM OR HURRICANE AT DAY 3.

HANNA CONTINUES TO MEANDER BUT THE BEST ESTIMATE OF AN INITIAL MOTION IS 250/05. SLOW AND ERRATIC MOTION IS EXPECTED TODAY BUT HANNA SHOULD START MOVING NORTHWESTWARD TONIGHT OR TOMORROW AS A LARGE MID-LATITUDE TROUGH OVER THE WESTERN ATLANTIC LIFTS NORTHWARD AND THE SUBTROPICAL RIDGE BUILDS BACK IN. HANNA SHOULD ACCELERATE NORTHWESTWARD AT DAYS 2 TO 3 AS THE RIDGE STRENGTHENS. DYNAMICAL TRACK MODELS HAVE SHIFTED A LITTLE TO THE WEST AND THE NEW OFFICIAL FORECAST FOLLOWS SUIT. ON THE FORECAST TRACK...HANNA IS EXPECTED TO APPROACH THE EAST COAST OF FLORIDA... GEORGIA...OR SOUTH CAROLINA IN 2 TO 3 DAYS. IT SHOULD BE STRESSED THAT THE EXPECTED ANGLE OF APPROACH AND TRACK UNCERTAINTY MAKE IT IMPOSSIBLE TO NARROW DOWN THE POTENTIAL IMPACT AREA. INTERESTS IN THE NORTHWESTERN BAHAMAS AND ALONG THE ENTIRE SOUTHEASTERN UNITED STATES COAST SHOULD CLOSELY MONITOR THE PROGRESS OF THIS SYSTEM.



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