New Update on Tropical Storm Ernesto – 10pm Saturday Update
August 4, 2012 Leave a comment
TROPICAL STORM ERNESTO DISCUSSION NUMBER 14
NWS NATIONAL HURRICANE CENTER MIAMI FL AL052012
1100 PM EDT SAT AUG 04 2012
DESPITE AN IMPRESSIVE APPEARANCE IN INFRARED IMAGERY…MICROWAVE IMAGERY AND REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE THAT ERNESTO HAS LOST SOME ORGANIZATION DURING THE PAST SEVERAL HOURS. THE MICROWAVE DATA SUGGESTS THAT THE LOW-LEVEL CENTER HAS BECOME PARTLY EXPOSED TO THE NORTHWEST OF THE STRONG CONVECTION…AND THE AIRCRAFT REPORTS THAT THE CENTRAL PRESSURE HAS RISEN TO 1007 MB. SINCE THE PLANE HAS NOT YET FULLY SAMPLED THE NORTHEASTERN QUADRANT WHERE THE STRONGEST WINDS WERE FOUND EARLIER…THE INITIAL INTENSITY IS HELD AT 50 KT. HOWEVER… IT IS POSSIBLE THAT THIS ESTIMATE IS GENEROUS.
THE LOW-LEVEL CENTER HAS ACCELERATED WEST-NORTHWESTWARD SINCE THE LAST ADVISORY…WITH A SHORT-TERM FORWARD SPEED OF OVER 20 KT. A LONGER-TERM MOTION IS 285/19…WHICH IS THE INITIAL MOTION FOR THE ADVISORY. THE REASON FOR THIS TRACK CHANGE IS UNCLEAR. HOWEVER… THE GUIDANCE IS IN GOOD AGREEMENT THAT ERNESTO SHOULD RESUME A WESTWARD MOTION DURING THE NEXT 12 HR OR SO ON THE SOUTH SIDE OF THE SUBTROPICAL RIDGE. AFTER 24-36 HR…THE RIDGE SHOULD GRADUALLY WEAKEN AS A MID/UPPER-LEVEL TROUGH DEVELOPS OVER THE EASTERN UNITED STATES. WHILE SOME SPREAD REMAINS…THE GUIDANCE HAS COME INTO BETTER AGREEMENT THAT ERNESTO WILL TURN WEST-NORTHWESTWARD AT A REDUCED FORWARD SPEED AFTER 36 HR…MOVING OVER THE YUCATAN PENINSULA OF MEXICO BETWEEN 72-96 HR AND REACHING THE SOUTHERN OR SOUTHWESTERN GULF OF MEXICO BY THE END OF THE FORECAST PERIOD. THE NEW FORECAST TRACK IS SHIFTED A LITTLE NORTH OF THE PREVIOUS TRACK THROUGH 24 HR DUE TO THE INITIAL MOTION. HOWEVER…IT HAS BEEN SHIFTED SOUTHWARD AFTER THAT TIME TO LIE NEAR THE VARIOUS CONSENSUS MODELS. OVERALL…THE NEW FORECAST TRACK IS FASTER THAN THE PREVIOUS TRACK.
IT IS ALSO UNCLEAR WHY ERNESTO HAS LOST ORGANIZATION SINCE THE OUTFLOW IS GOOD IN ALL DIRECTIONS…THE VERTICAL WIND SHEAR IS LIGHT…AND THE SEA SURFACE TEMPERATURES ARE WARM. ONE POSSIBLE CAUSE MIGHT BE DRY AIR SEEN IN WATER VAPOR IMAGERY WEST OF THE CYCLONE. THE DYNAMICAL GUIDANCE CONTINUES TO SUGGEST THAT ERNESTO WILL NOT STRENGTHEN MUCH BEFORE REACHING THE NORTHWESTERN CARIBBEAN…WHILE THE STATISTICAL-DYNAMICAL MODELS CONTINUE TO FORECAST STEADY STRENGTHENING THROUGH THE FORECAST PERIOD. GIVEN THE TRENDS DURING THE PAST 24 HR…THE NEW INTENSITY FORECAST CALLS FOR A LOWER INTENSIFICATION RATE THAN THE PREVIOUS ADVISORY…WITH ERNESTO BECOMING A HURRICANE IN 48 HR. GIVE THE DIVERGENT GUIDANCE…THE INTENSITY FORECAST REMAINS OF LOW CONFIDENCE.
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