Replies

Here ya go, folks. Hot off the presses. No real change in heading.
And no, I'm not yelling.

717
WTNT43 KNHC 120226
TCDAT3

HURRICANE ISABEL DISCUSSION NUMBER 24
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT THU SEP 11 2003

ISABEL LOOKS LIKE IT IS ABOUT TO BEGIN AN EYEWALL REPLACEMENT CYCLE. AN AMSU MICROWAVE PASS AT 1737Z SHOWED THREE-FOURTHS OF AN OUTER EYEWALL. AT 2313Z...AN SSMI PASS SHOWED TWO CONCENTRIC EYEWALLS...WITH SOME EROSION ON THE NORTH SIDE OF THE INNER EYEWALL. THIS IS CONSISTENT WITH CONVENTIONAL IR IMAGERY WHICH ALSO SHOWS CONSIDERABLE WARMING OF THE CONVECTION IN THE NORTH EYEWALL OVER THE PAST SEVERAL HOURS. THE RELATIVELY LIGHT WIND EYE AND MOAT BETWEEN THE TWO EYEWALLS CAN EVEN BE SEEN IN THE RAW RETURNED SIGNAL FROM THE QUIKSCAT SCATTEROMETER PASS AT 2116Z. WHAT THIS MOST LIKELY MEANS IS THAT THE HURRICANE WILL WEAKEN OVER THE NEXT 12 HOURS OR SO AS THE INNER EYEWALL COLLAPSES...BUT THEN COULD REINTENSIFY AFTER THAT AS THE OUTER EYEWALL CONTRACTS. WE DO NOT NORMALLY TRY TO INCLUDE THESE KINDS OF FLUCTUATIONS IN THE OFFICIAL INTENSITY FORECAST...BUT BECAUSE THIS REPLACEMENT SEEMS TO BE UNDERWAY I HAVE TAKEN A SHOT AT IT. REGARDLESS OF HOW THE CORE STRUCTURE EVOLVES IN THE NEAR TERM...ISABEL IS EXPECTED TO REMAIN A MAJOR HURRICANE THROUGHOUT THE FORECAST PERIOD. RECENT SST ANALYSES SHOW THAT THE COOL WAKE OF FABIAN IS GRADUALLY DIMINISHING AND MAY NOT HAVE A SIGNIFICANT EFFECT ON ISABEL.

A SLIGHT WOBBLE TO THE LEFT IS OCCURRING AT THE MOMENT...BUT THE LONG-TERM MOTION REMAINS 280/8. THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE SYNOPTIC THINKING...SHORT-RANGE MODEL GUIDANCE...OR OFFICIAL TRACK FORECAST. A DEEP-LAYER HIGH PRESSURE AREA TO THE NORTH OF ISABEL IS LIKELY TO MAINTAIN THE SLOW WESTWARD TO WEST-NORTHWESTWARD STEERING OVER THE NEXT SEVERAL DAYS. BEYOND THE 5-DAY FORECAST PERIOD...MODEL GUIDANCE BEGINS TO DIVERGE AS STEERING CURRENTS WEAKEN. IT IS STILL TOO EARLY TO SPECULATE WHAT PORTIONS OF THE U.S. EAST COAST MIGHT BE AFFECTED BY ISABEL.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 12/0300Z 21.6N 56.1W 140 KT
12HR VT 12/1200Z 21.9N 57.5W 130 KT
24HR VT 13/0000Z 22.3N 59.4W 135 KT
36HR VT 13/1200Z 22.7N 61.3W 130 KT
48HR VT 14/0000Z 23.3N 63.2W 125 KT
72HR VT 15/0000Z 24.5N 66.5W 115 KT
96HR VT 16/0000Z 25.5N 69.5W 115 KT
120HR VT 17/0000Z 26.5N 72.5W 110 KT

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

From the TPC:000
WTNT33 KNHC 120843
TCPAT3
BULLETIN
HURRICANE ISABEL ADVISORY NUMBER 25
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM AST FRI SEP 12 2003

...EXTREMELY DANGEROUS HURRICANE ISABEL CONTINUES ON A WESTWARD
TRACK...

AT 5 AM AST...0900Z...THE EYE OF HURRICANE ISABEL WAS LOCATED NEAR
LATITUDE 21.7 NORTH...LONGITUDE 57.0 WEST OR ABOUT 455 MILES...730
KM...EAST-NORTHEAST OF THE NORTHERN LEEWARD ISLANDS.

ISABEL IS MOVING TOWARD THE WEST NEAR 9 MPH ...15 KM/HR. THIS
GENERAL TRACK IS EXPECTED TO CONTINUE DURING THE NEXT 24 HOURS

MAXIMUM SUSTAINED WINDS REMAIN NEAR 160 MPH...260 KM/HR...WITH
HIGHER GUSTS. SOME TEMPORARY WEAKENING IS POSSIBLE TODAY.
FLUCTUATIONS IN INTENSITY ARE COMMON IN MAJOR HURRICANES.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 60 MILES... 95 KM...
FROM THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP
TO 185 MILES...295 KM.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 921 MB...27.20 INCHES.

LARGE OCEAN SWELLS AND DANGEROUS SURF CONDITIONS ARE LIKELY OVER
PORTIONS OF THE LEEWARD ISLANDS...THE VIRGIN ISLANDS...AND PUERTO
RICO OVER THE NEXT SEVERAL DAYS.

REPEATING THE 5 AM AST POSITION...21.7 N... 57.0 W. MOVEMENT
TOWARD...WEST NEAR 9 MPH. MAXIMUM SUSTAINED WINDS...160 MPH.
MINIMUM CENTRAL PRESSURE... 921 MB.

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
11 AM AST.

FORECASTER AVILA

000
WTNT43 KNHC 120843
TCDAT3
HURRICANE ISABEL DISCUSSION NUMBER 25
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT FRI SEP 12 2003

THERE ARE NO NEW CHANGES TO REPORT OR THAT CAN BE ADDED TO THE
STRUCTURE AND INTENSITY OF ISABEL AFTER THE PREVIOUS DISCUSSION.
BASED ON THE OUSTANDING CLOUD PATTERN...SATELLITE INTENSITY
ESTIMATES STILL SUPPORT 140 KNOTS. REGARDLESS OF HOW THE CORE
STRUCTURE EVOLVES IN THE NEAR TERM...ISABEL IS EXPECTED TO REMAIN A
MAJOR HURRICANE THROUGHOUT THE FORECAST PERIOD.

HERE COMES A LITTLE DISCUSSION ABOUT THE FOUR MAIN MODELS. THE GFDL
WHICH HAS BEEN PERFORMING QUITE WELL...TURNS THE HURRICANE MORE TO
THE NORTHWEST AND NORTH-NORTHWEST...AND DEPENDING UPON THE RUN YOU
PICK...THE TURN OCCURS FARTHER TO THE WEST OR FARTHER TO THE EAST.
ON THE OTHER HAND...THE UK MODEL WHICH HAS HAS BEEN MORE CONSISTENT
...MOVES THE HURRICANE FASTER AND BRING ISABEL DANGEROUSLY CLOSE TO
THE U.S. COAST IN 5 DAYS. THE GFS WHICH HAS BEEN CHANGING ITS TUNE
FROM RUN TO RUN...IS MUCH SLOWER AND IN 5 DAYS PLACES THE HURRICANE
ABOUT 450 N MI FROM THE U.S COAST. THE GFS EVENTUALLY BRINGS THE
CENTER NEAR THE COAST OF NORTH CAROLINA IN SEVERAL MORE DAYS.
FINALLY...THE NOGAPS IS VERY SIMILAR TO THE GFS UP TO 5 DAYS.

NOTE: THEY ALL HAVE IN COMMON THE DEVELOPMENT AND THE WESTWARD
EXPANSION OF A STRONG RIDGE TO THE NORTH OF THE HURRICANE BEYOND 5
DAYS. IF THIS PATTERN EVOLVES...THE HURRICANE COULD POSE A
SIGNIFICANT THREAT TO THE U.S. EAST COAST.

HAVING SAID ALL THAT...HERE COMES THE OFFICIAL FORECAST. ISABEL HAS
BEEN MOVING TOWARD THE WEST OR 270 DEGREES AT 8 KNOTS AROUND A
DEEP-LAYER SUBTROPICAL HIGH. THIS PATTERN WOULD FAVOR A WEST TO
WEST-NORTHWEST TRACK THROUGH 5 DAYS WITH NO SIGNIFICANT CHANGE IN
FORWARD SPEED. MOST IMPORTANTLY...DUE TO THE LARGE VARIATION IN
MODELS FROM RUN TO RUN...IT IS TOO EARLY TO SPECULATE WHAT PORTIONS
OF THE U.S. EAST COAST MIGHT BE AFFECTED BY ISABEL.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 12/0900Z 21.7N 57.0W 140 KT
12HR VT 12/1800Z 22.0N 58.4W 130 KT
24HR VT 13/0600Z 22.5N 60.5W 135 KT
36HR VT 13/1800Z 23.0N 62.5W 130 KT
48HR VT 14/0600Z 23.5N 64.5W 125 KT
72HR VT 15/0600Z 25.0N 69.0W 115 KT
96HR VT 16/0600Z 26.0N 71.5W 115 KT
120HR VT 17/0600Z 27.5N 74.0W 110 KT