Hurricane IVAN Discussion 27

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Hurricane IVAN

 

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WTNT44 KNHC 090231

TCDAT4

HURRICANE IVAN DISCUSSION NUMBER 27

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL

11 PM EDT WED SEP 08 2004

 

IVAN WENT THROUGH A PERIOD OF RAPID DEEPENING THIS AFTERNOON...WITH

THE CENTRAL PRESSURE FALLING FROM 951 TO 938 MB IN A PERIOD OF

ABOUT 5.5 HOURS. THE MAXIMUM 700 MB FLIGHT LEVEL-WINDS WERE 131

KT...AND A NORTHEAST EYEWALL DROPSONDE SUGGESTED SURFACE WINDS NEAR

120 KT. BASED ON THE DROPSONDE AND THE PRESSURE...THE MAXIMUM

INTENSITY IS INCREASED TO 125 KT...WHICH IS IN GOOD AGREEMENT WITH

127 KT SATELLITE INTENSITY ESTIMATES FROM TAFB...SAB...AND AFWA.

THE SATELLITE SIGNATURE OF THE HURRICANE HAS NOT CHANGED

SIGNIFICANTLY SINCE THE HURRICANE HUNTER LEFT...SO IT IS UNKNOWN IF

THE DEEPENING HAS CONTINUED. THE INITIAL INTENSITY COULD BE A

LITTLE CONSERVATIVE.

 

IVAN HAS NUDGED A LITTLE TO THE LEFT DURING THE EVENING AND THE

INITIAL MOTION IS NOW 290/15. THERE IS LITTLE CHANGE TO THE

FORECAST PHILOSOPHY DURING THE FIRST 48 HR...AS IVAN SHOULD

CONTINUE WEST-NORTHWESTWARD TOWARD JAMAICA ON THE SOUTH SIDE OF THE

SUBTROPICAL RIDGE. THINGS GETS MORE UNCERTAIN AFTER 48 HR...AS THE

RIDGE STARTS TO WEAKEN DUE TO A DIGGING MID/UPPER-LEVEL TROUGH OVER

THE EASTERN UNITED STATES AND AN UPPER-LEVEL LOW MOVING WESTWARD

UNDER THE RIDGE. THIS COMBINATION SHOULD ALLOW IVAN TO TURN

NORTHWESTWARD AND EVENTUALLY NORTHWARD...WITH THE USUAL QUESTIONS

OF WHERE AND WHEN. THE GFS...GFDL...NOGAPS...AND FSU SUPERENSEMBLE

HAVE ALL SHIFTED TO THE RIGHT...WITH THE GFS RECURVING IVAN THROUGH

THE BAHAMAS...THE GFDL MOVING IT INTO SOUTHEASTERN FLORIDA...THE

NOGAPS MOVING IT UP THE LENGTH OF THE FLORIDA PENINSULA...AND THE

SUPERENSEMBLE PASSING JUST WEST OF KEY WEST. GIVEN THE

INCONSISTENCY OF THE MODELS...AND THE LEFTWARD NUDGE THAT OCCURRED

THIS EVENING...THE FORECAST TRACK WILL NOT SHIFT AS FAR EAST AS THE

GUIDANCE AT THIS TIME. THE NEW TRACK IS SHIFTED A LITTLE WEST OF

THE PREVIOUS TRACK FOR THE FIRST 24-36 HR AND THEN SOMEWHAT TO THE

RIGHT AFTER 72 HR.

 

THE INTENSITY FORECAST CALLS FOR IVAN TO REACH 135 KT IN 12 HR ON

THE PREMISE THAT THE AFTERNOON STRENGTHENING WILL CONTINUE. AFTER

THAT...VARIOUS ANALYSES INDICATE THAT IVAN SHOULD PASS OVER COOLER

SEA SURFACE TEMPERATURES AND REDUCED MAXIMUM POTENTIAL INTENSITY

FOR ABOUT 24 HR. THIS COMBINED WITH AN EXPECTED CONCENTRIC EYEWALL

CYCLE SHOULD CAUSE SOME WEAKENING. WARMER WATER AWAITS OVER THE

NORTHWESTERN CARIBBEAN AND THE STRAITS OF FLORIDA...WHICH WOULD

ALLOW SOME STRENGTHENING WHEN IVAN IS NOT HITTING LAND OR

UNDERGOING CONCENTRIC EYEWALL CYCLES. AFTER 96 HR...SOME WESTERLY

SHEAR MAY DEVELOP AND THE INTENSITY FORECAST REFLECTS A SLIGHT

WEAKENING AT 120 HR. WHILE THE INTENSITY UPS AND DOWNS MAY BE MORE

PRONOUNCED THAN FORECAST HERE...IVAN IS EXPECTED TO REMAIN A MAJOR

HURRICANE THROUGH THE FORECAST PERIOD.

 

FORECASTER BEVEN

 

FORECAST POSITIONS AND MAX WINDS

 

INITIAL 09/0300Z 13.6N 69.1W 125 KT

12HR VT 09/1200Z 14.5N 71.0W 135 KT

24HR VT 10/0000Z 15.9N 73.4W 130 KT

36HR VT 10/1200Z 17.4N 75.6W 125 KT

48HR VT 11/0000Z 18.6N 77.5W 120 KT...NEAR JAMAICA

72HR VT 12/0000Z 21.0N 80.0W 125 KT

96HR VT 13/0000Z 23.5N 82.0W 120 KT

120HR VT 14/0000Z 27.0N 82.5W 115 KT

 

 

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