BULLETIN
HURRICANE BERTHA ADVISORY NUMBER 28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008
11:00 PM AST WED JUL 09 2008
BERTHA EXPECTED TO MOVE MORE SLOWLY BUT COULD REGAIN MAJOR HURRICANE
STATUS... IT IS STILL TOO EARLY TO DETERMINE THE EXTENT TO WHICH BERTHA
COULD IMPACT BERMUDA. INTERESTS ON THAT ISLAND SHOULD CLOSELY MONITOR THE
PROGRESS OF BERTHA DURING THE NEXT SEVERAL DAYS.
AT 11:00 PM AST, 3:00Z, THE CENTER OF HURRICANE BERTHA WAS LOCATED NEAR
LATITUDE 25.5 NORTH, LONGITUDE 58.9 WEST, OR ABOUT 590 MILES, 950 KM
SOUTHEAST OF BERMUDA. BERTHA IS MOVING TOWARD THE NORTHWEST NEAR 12 MPH, 19
KM HR. A GRADUAL TURN TOWARD THE NORTH WITH A DECREASE IN FORWARD SPEED IS
EXPECTED DURING THE NEXT COUPLE OF DAYS. MAXIMUM SUSTAINED WINDS ARE NEAR
105 MPH, 165 KM HR, WITH HIGHER GUSTS. BERTHA IS A CATEGORY TWO HURRICANE
ON THE SAFFIR-SIMPSON SCALE. SOME STRENGTHENING IS FORECAST DURING THE NEXT
24 HOURS, AND BERTHA COULD REGAIN MAJOR HURRICANE STATUS ON THURSDAY.
HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 30 MILES, 45 KM FROM THE CENTER,
AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 140 MILES, 220 KM.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 970 MB, 28.64 INCHES. LARGE SWELLS AND
HIGH SURF ARE EXPECTED TO AFFECT PORTIONS OF BERMUDA DURING THE NEXT FEW
DAYS.
REPEATING THE 11:00 PM AST POSITION, 25.5 N, 58.9 W. MOVEMENT TOWARD
NORTHWEST NEAR 12 MPH. MAXIMUM SUSTAINED WINDS, 105 MPH. MINIMUM CENTRAL
PRESSURE, 970 MB. THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE
CENTER AT 5:00 AM AST.
HURRICANE BERTHA DISCUSSION NUMBER 28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022008
11:00 PM EDT WED JUL 09 2008
THERE HAVE BEEN NO APPRECIABLE CHANGES IN THE SATELLITE APPEARANCE OF THE
HURRICANE DURING THE PAST FEW HOURS. OBJECTIVE DVORAK ESTIMATES APPROACHED
100 KT A FEW HOURS AGO, BUT HAVE SINCE COME BACK DOWN IN LINE WITH THE 00Z
SUBJECTIVE ESTIMATES, WHICH SUPPORT MAINTAINING THE ADVISORY INTENSITY AT 90
KT. BERTHA CURRENTLY LIES OVER SEA-SURFACE TEMPERATURES OF ALMOST 28
CELSIUS, AND THE WATERS ALONG THE FORECAST TRACK WILL REMAIN ABOUT THE SAME
FOR THE NEXT COUPLE OF DAYS. GLOBAL MODELS DO NOT APPEAR TO FORECAST AN
INCREASE IN VERTICAL WIND SHEAR IMPACTING THE TROPICAL CYCLONE DURING THAT
PERIOD, SO ALL OF THE OBJECTIVE INTENSITY MODELS FORECAST AT LEAST A LITTLE
STRENGTHENING. THE OFFICIAL FORECAST AGAIN CALLS FOR BERTHA TO REGAIN MAJOR
HURRICANE STATUS, IN AGREEMENT WITH THE HWRF MODEL. GRADUAL WEAKENING IS
FORECAST AT DAYS 3 THROUGH 5 DUE TO COOLING SSTS AND THE POTENTIAL FOR AN
INCREASE IN SHEAR IN LINE WITH THE INTENSITY MODEL CONSENSUS. THE SHIPS AND
LGEM, HOWEVER, FORECAST MORE RAPID WEAKENING THAN THE GFDL AND HWRF. SO HOW
MUCH WEAKENING OCCURS NEAR THE END OF THE FORECAST IS RATHER UNCERTAIN, AND
DEPENDS IN PART ON HOW FAST BERTHA MOVES TOWARD COOLER WATERS BY THAT TIME.
THE HURRICANE CONTINUES MOVING NORTHWESTWARD, OR ALONG 315 DEGREES AT ABOUT
10 KT WITH STEERING PROVIDED BY A MID-LEVEL RIDGE TO ITS NORTH. AS THAT
RIDGE SLIDES EASTWARD AND WEAKENS DURING THE NEXT TWO TO THREE DAYS, BERTHA
IS FORECAST TO GRADUALLY TURN TOWARD THE NORTH AND SLOW DOWN. THIS PORTION
OF THE FORECAST IS AGREED UPON WELL BY THE VARIOUS DYNAMICAL MODELS, BUT
THEN THEY START TO DIVERGE, ESPECIALLY IN TERMS OF FORWARD SPEED DUE TO
VARYING DEPICTIONS OF WHEN A HIGH-AMPLITUDE TROUGH WILL EMERGE OFF THE EAST
COAST OF THE UNITED STATES. THE UKMET, NOGAPS AND GFDL FORECAST BERTHA TO
SPEED UP BEYOND 72 HOURS AHEAD OF A SLIGHTLY MORE PROGRESSIVE TROUGH, WHILE
THE 18Z GFS AND THE 12Z ECMWF FORECAST BERTHA TO STALL AT 72-120 HOURS,
WAITING FOR THAT TROUGH TO PERHAPS PICK BERTHA UP LATER. THE NEW OFFICIAL
TRACK FORECAST IS SLOWED DOWN A LITTLE AT THE END COMPARED TO THE PREVIOUS
ADVISORY AS AN APPROXIMATE COMPROMISE BETWEEN THESE EXTREMES. IT IS
IMPORTANT TO NOTE THAT ALL OF THE MODELS SHOW A RELATIVELY SLOW MOTION AT
AROUND 72 HOURS, NOT FAR EAST OF BERMUDA AND BERTHA COULD MOVE ERRATICALLY
DURING THAT TIME FRAME. THEREFORE, INTERESTS ON THAT ISLAND SHOULD CLOSELY
MONITOR THE PROGRESS OF BERTHA FOR THE NEXT SEVERAL DAYS.
CONSIDERING THE COMBINED FORECAST UNCERTAINTIES IN THE TRACK, INTENSITY AND
SIZE OF BERTHA, THERE IS ALREADY A 43% CHANCE THAT BERMUDA WILL EXPERIENCE
SUSTAINED WINDS OF TROPICAL STORM FORCE DURING THE NEXT FIVE DAYS AS
CONVEYED IN THE WIND SPEED PROBABILITY PRODUCT ACCOMPANYING THIS ADVISORY
PACKAGE.
This information is provided as a public service from the
National Hurricane Center
http://www.nhc.noaa.gov
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