000
AGXX40 KNHC 300800
MIMATS

MARINE WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
400 AM EDT TUE APR 30 2013

MARINE WEATHER DISCUSSION FOR THE GULF OF MEXICO...CARIBBEAN
SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN 55W AND
64W...AND THE SW N ATLANTIC INCLUDING THE BAHAMAS.

...GULF OF MEXICO...
MODEL PREFERENCE: GFS/ECMWF OVERALL WITH AVERAGE CONFIDENCE.
SECTORIZED GFS IN WESTERN GULF TO CAPTURE HIGHER WINDS BEHIND
FRONT MORE IN LINE WITH SREF OUTPUT. ALSO ALTERED MWW3 OUTPUT IN
WESTERN GULF TO MIRROR EC WAVE IN ORDER TO SHOW MORE RAPID IN POST
FRONTAL WAVE GROWTH.

CURRENT PATTERN SHOWS AN ELONGATED UPPER TROUGH FROM THE UPPER
MISSISSIPPI VALLEY THROUGH WEST TEXAS WITH AN EMBEDDED UPPER LOW
OVER S CENTRAL TEXAS. THIS IS SUPPORTING CLUSTERS OF CONVECTION
ACROSS THE NW GULF ATTM. THIS FEATURE MIGRATES EASTWARD ACROSS THE
NORTHERN GULF THROUGH TODAY WITHIN AN ACTIVE SOUTHERN STREAM
JET...AHEAD OF AN AMPLIFYING LONGWAVE TROUGH MOVING OUT OF THE
ROCKIES AND INTO THE CENTRAL PLAINS THROUGH THU. AN ATTENDANT COLD
FRONT WILL PUSH OFF THE TEXAS COAST BY LATE FRI. THERE REMAIN
DECENT CONSISTENCY IN THE MODELS CONCERNING THE TIMING OF THE
FRONT INTO THE NW GULF. LESS CERTAIN HAS BEEN THE LIKELIHOOD OF
WINDS TO GALE FORCE BEHIND THE FRONT ALONG THE MEXICAN COAST. THIS
REMAINS THE MAIN FORECAST CHALLENGE. GEFS GUIDANCE OVER THE PAST
24 TO 36 HOURS HAS TRENDED LOWER ON THE CHANCES FOR GALES OVER THE
FAR SW GULF ALONG THE COAST OF VERACRUZ...BUT HAS BEEN
ALTERNATING ON WHETHER GALE WILL OCCUR FARTHER NORTH NEAR
TAMPICO. IN ADDITION...THE PAST COUPLE OF RUNS OF THE SREF ALSO
FAVOR GALES OFF TAMPICO...WITH 50% PROBABILITIES. WITH THIS...HAVE
REINSTATED GALE CONDITIONS EXPECTED FOR GMZ017 OFF THE SOUTHERN
COAST OF TAMAULIPAS. MORE TROUBLING IS WHAT TO DO ABOUT GMZ023
ALONG THE COAST OF VERACRUZ. GEFS OUTPUT IS CONSISTENTLY NEGATIVE
ON GALES AS ARE ALL OPERATIONAL RUNS. BUT SREF GUIDANCE REMAINS
BULLISH WITH 50% PROBABILITIES. GIVEN THE HIGH SUN ANGLES THIS
TIME OF YEAR QUICKLY MODIFYING COOL AIRMASSES MOVING INTO THE
GULF...WILL HOLD OFF ON GALES FOR VERACRUZ. MWW3 OUTPUT IS
TYPICALLY TOO SLOW WITH POST FRONTAL WAVE GROWTH...SO MADE
ADJUSTMENTS UPWARD OVER THE NW GULF MORE IN LINE WITH EC WAVE AND
UKMET WAVE FOR LATE THU AND FRI NIGHT. MEANWHILE...OFFSHORE FLOW
CONTINUES TO DELIVER AREAS OF SMOKE FROM FOREST FIRES LIMITING
VISIBILITIES ALONG THE CAMPECHE COAST. FOR SAT...THE FRONT WEAKENS
AS IT SHIFTS FARTHER SE AND WASHES OUT BY LATE SAT FROM THE
FLORIDA BIG BEND TO THE CENTRAL GULF. WINDS AND SEAS DIMINISH
ACCORDINGLY AS HIGH PRES BUILDS BEHIND THE FRONT OVER THE NW GULF.

...CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN
55W AND 64W...
MODEL PREFERENCE: GFS/ECMWF/PERSISTENCE BLEND WITH GOOD
CONFIDENCE.

HIGH PRES N OF REGION WILL MAINTAIN MODERATE TO FRESH BREEZES
ACROSS TROPICAL N ATLC AND CENTRAL CARIBBEAN WITH GENTLE TO
MODERATE E FLOW THROUGH MID WEEK. FRESH BREEZES EXPECTED ACROSS
GULF OF HONDURAS TUE THROUGH THU AS RIDGE STRENGTHENS BEFORE
DRIFTING E. LONG PERIOD NE SWELL 5-6 FT SEEP THROUGH ATLC PASSAGES
TODAY AND TONIGHT THEN BEGINNING SUBSIDING THROUGH WED. WINDS
DIMINISH ACROSS THE BASIN LATER IN THE WEEK AS THE HIGH PRES N OF
THE AREA SHIFTS E AND IS REPLACED BY LOW PRES...THUS WEAKENING THE
PRES GRADIENT OVER THE REGION. A BLEND OF GFS/ECMWF IS THE BASIS
FOR THE GRIDS.

...SW N ATLANTIC INCLUDING THE BAHAMAS...
MODEL PREFERENCE: GFS/ECMWF BLEND WITH AVERAGE CONFIDENCE IN THE
SHORT TERM AND LOW CONFIDENCE LATE IN THE PERIOD.

THE PATTERN WILL START TO TRANSITION TODAY AS WEAK HIGH PRES
CENTERED JUST W OF BERMUDA WILL START TO SHIFT E AHEAD OF WEAK LOW
PRES DEVELOPING OVER THE CAROLINAS SHIFTING SE INTO THE DISCUSSION
AREA. GFS/ECMWF/UKMET ARE IN DECENT AGREEMENT SHOWING THE LOW PRES
FORMING AND DRIFTING TO GIVE/TAKE 31N77W WED...BEFORE OPENING
INTO A TROUGH BY LATE WED. THE MAIN ISSUE IS THE ENHANCED GRADIENT
ON THE NORTH SIDE OF THE LOW/TROUGH WHICH IS CAPTURED WELL BY ALL
MODELS. THE APPROACH OF THE LONGWAVE TROUGH INTO THE MISSISSIPPI
VALLY BY FRI/SAT WILL SPUR LOW DEVELOPMENT NEAR SOUTH
FLORIDA...ALTHOUGH THERE IS STILL POOR MODEL CONSENSUS ON EXACT
CENTER POSITION OR INTENSITY ATTM. KEPT A GFS/ECMWF BLEND FOR NOW.

.WARNINGS...ANY CHANGES IMPACTING COASTAL NWS OFFICES WILL BE
COORDINATED THROUGH AWIPS 12 PLANET CHAT OR BY TELEPHONE:

.GULF OF MEXICO...
GMZ011...NONE.
GMZ013...NONE.
GMZ015...NONE.
GMZ017...GALE CONDITIONS EXPECTED FRI.
GMZ019...NONE.
GMZ021...NONE.
GMZ023...NONE.
GMZ025...NONE.

.CARIBBEAN SEA AND TROPICAL N ATLANTIC FROM 07N TO 19N BETWEEN
55W AND 64W...
AMZ011...NONE.
AMZ013...NONE.
AMZ015...NONE.
AMZ017...NONE.
AMZ019...NONE.
AMZ021...NONE.
AMZ023...NONE.
AMZ025...NONE.
AMZ027...NONE.
AMZ029...NONE.
AMZ031...NONE.
AMZ033...NONE.
AMZ035...NONE.
AMZ037...NONE.
AMZ039...NONE.

.SW N ATLANTIC INCLUDING THE BAHAMAS...
AMZ111...NONE.
AMZ113...NONE.
AMZ115...NONE.
AMZ117...NONE.
AMZ119...NONE.
AMZ121...NONE.
AMZ123...NONE.
AMZ125...NONE.
AMZ127...NONE.

*FOR DETAILED ZONE DESCRIPTIONS PLEASE VISIT:
HTTP://WWW.NHC.NOAA.GOV/ABOUTTAFBPROD.SHTML#OWF

NOTE: GRIDDED MARINE FORECASTS ARE AVAILABLE IN THE
NATIONAL DIGITAL FORECAST DATABASE (NDFD) AT:
HTTP://WWW.NHC.NOAA.GOV/MARINE/GRIDS.PHP

FOR ADDITIONAL INFORMATION PLEASE VISIT:
HTTP://WWW.HURRICANES.GOV/MARINE

$$
.FORECASTER CHRISTENSEN. NATIONAL HURRICANE CENTER.