[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 131051 AAA
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT WED SEP 13 2006

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHEASTERN
SECTIONS OF SOUTH AMERICA...AND THE ATLANTIC OCEAN TO THE
AFRICAN COAST FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION
IS BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...
AND METEOROLOGICAL ANALYSIS.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1030 UTC.

...SPECIAL FEATURES...
THE CENTER OF HURRICANE GORDON AT 13/0900 UTC WAS NEAR 25.1N
57.9W OR ABOUT 605 NM/975 KM NORTH-NORTHEAST OF THE LEEWARD
ISLANDS. GORDON IS MOVING NORTHWARD AT 8 KT AND THIS MOTION IS
EXPECTED TO CONTINUE FOR THE NEXT 24 HOURS. THE ESTIMATED
MINIMUM CENTRAL PRESSURE IS 987 MB. THE MAXIMUM SUSTAINED WIND
SPEEDS ARE 65 KT WITH GUSTS TO 80 KT....THIS MAKES GORDON A
CATEGORY ONE HURRICANE ON THE SAFFIR-SIMPSON SCALE.  PLEASE READ
THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT2/WTNT22 KNHC AND THE PUBLIC ADVISORY MIATCPAT2/WTNT32
KNHC FOR MORE DETAILS. A RAGGED EYE...ABOUT 40-50 NM IN
DIAMETER...HAS BECOME EVIDENT ON INFRARED SATELLITE IMAGERY
DURING THE OVERNIGHT HOURS. CONVECTIVE BANDS AND AN EYEWALL
FEATURE HAS ALSO BECOME MORE APPARENT WITH THE STORM LOOKING
INCREASINGLY MORE SYMMETRIC. IN ADDITION...THE OUTFLOW LAYER HAS
BECOME IMPRESSIVE AND IS ONLY SLIGHTLY RESTRICTED TO THE E/SE.
GORDON REMAINS A VERY COMPACT HURRICANE WITH ITS RAIN FIELD
WITHIN 150 NM OF THE CENTER. HURRICANE FORCE WINDS EXTEND
OUTWARD WITHIN 20 NM IN THE NE QUADRANT AND TROPICAL STORM FORCE
WINDS WITHIN 75 NM. SOME ADDITIONAL STRENGTHENING IS FORECAST
DURING THE NEXT 24 HOURS. GORDON IS ALREADY ON THE NORTHWESTERN
PERIPHERY OF THE SUBTROPICAL RIDGE AND EXPECTED TO REMAIN IN THE
OPEN ATLANTIC.

THE CENTER OF TROPICAL DEPRESSION EIGHT AT 13/0900 UTC WAS NEAR
11.9N 26.7W OR ABOUT 255 NM/405 KM SOUTHWEST OF THE SOUTHERNMOST
CAPE VERDE ISLANDS. T.D. EIGHT IS MOVING WEST AT 14 KT AND THIS
GENERAL MOTION IS EXPECTED TO CONTINUE FOR THE NEXT 24 HOURS
WITH A GRADUAL INCREASE IN FORWARD SPEED. THE ESTIMATED MINIMUM
CENTRAL PRESSURE IS 1007 MB. THE MAXIMUM SUSTAINED WINDS REMAIN
NEAR 30 KT WITH GUSTS TO 40 KT. PLEASE READ THE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC
AND THE PUBLIC ADVISORY MIATCPAT3/WTNT33 KNHC FOR MORE DETAILS.
UNLIKE GORDON...T.D. EIGHT IS A VERY BROAD ELONGATED GYRE WITH
ITS CYCLONIC FLOW ENVELOPE COVERING A REGION OF SEVERAL HUNDRED
NM WIDE. MULTIPLE LOW LEVEL SWIRLS ARE EVIDENT ON EARLY MORNING
VIS IMAGES. CONVECTION IS LIMITED NEAR THE CENTER OF THE BROAD
CIRCULATION...HOWEVER THERE ARE AREAS OF MODERATE TO STRONG
CONVECTION TO THE NORTH AND WEST OF THE CENTER WITH THE COLDEST
CLOUD TOPS NEAR -85C TO THE NW OF THE CENTER. A FAIR AMOUNT OF
SAHARAN DUST LIES TO THE NORTH OF THE CYCLONE. DUE TO THIS
INHIBITING FACTOR AND BECAUSE T.D. EIGHT IS LARGE/BROAD AND WILL
TAKE SOME TIME TO CONSOLIDATE...ONLY SLOW STRENGTHENING IS
FORECAST OVER THE NEXT 24 HOURS.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 41W SOUTH OF 15N MOVING WEST 10 TO 15
KT. THERE IS SOME SLIGHT LOW TO MID LEVEL CYCLONIC TURNING IN
THE SMALL AREA OF SCATTERED SHOWERS AND TSTMS JUST AHEAD OF THE
ANALYZED AXIS FROM 6N-8N BETWEEN 42W-45W. TWO SHIP OBSERVATION
HAVE BEEN VERY HELPFUL IN LOCATING THE AXIS AS THEY HAVE
INDICATED A WEAK WAVE PASSAGE. OVERALL...THIS WAVE IS POORLY
STRUCTURED AND IS NOT IN A CONDUCIVE UPPER LEVEL ENVIRONMENT FOR
SIGNIFICANT DEVELOPMENT DUE TO THE CLOSE PROXIMITY OF T.D.
EIGHT.

A TROPICAL WAVE IS ALONG 50W SOUTH OF 14N MOVING WEST NEAR 10 KT
OVER THE LAST 24 HOURS. THIS WAVE HAS BEEN CHALLENGING TO TRACK
AS IT CONTINUES TO BE A LOW AMPLITUDE FEATURE. THIS FEATURE IS
BARELY IDENTIFIABLE ON SATELLITE IMAGERY...SURFACE OBS AND
QUIKSCAT DATA. SCATTERED SHOWERS AND TSTMS ARE NEAR THE BASE OF
THE ANALYZED AXIS FROM 4N-6N BETWEEN 47W-51W.

A WELL-DEFINED HIGH AMPLITUDE TROPICAL WAVE IS ALONG 58W SOUTH
OF 18N MOVING WEST 10 TO 15 KT. UNLIKE THE TWO WAVES TO ITS
EAST...THIS ONE IS VERY EASY TO FIND WITH A CLASSIC INVERTED
V-SHAPE SEEN ON SATELLITE IMAGES. SCATTERED MODERATE CONVECTION
IS INCREASING IN INTENSITY AND COVERAGE WITHIN 300 NM OF THE
WAVE AXIS. SOME OF THE DEEPEST MOISTURE IS OVER THE WINDWARD
ISLANDS.

A TROPICAL WAVE IS IN THE CARIBBEAN ALONG 69W SOUTH OF 16N
MOVING WEST NEAR 15 KT. THIS WAVE IS WEAK WITH ONLY A SLIGHT
HINT OF LOW-MID CYCLONIC TURNING NEAR THE WAVE AXIS. CONVECTION
IS MOSTLY INLAND OVER SOUTH AMERICA ASSOCIATED WITH THE ITCZ.

...THE ITCZ...
ITCZ IS CENTERED ALONG 15N17W 9N28W 7N40W 8N49W 13N59W 11N67W.
BESIDES FOR THE CONVECTION ASSOCIATED WITH T.D. EIGHT AND THE
TROPICAL WAVES...SCATTERED MODERATE CONVECTION IS OVER WRN
COLOMBIA FROM 3N-11N BETWEEN 71W-78W.

...DISCUSSION...

THE GULF OF MEXICO...
A 1010 MB LOW HAS FORMED JUST SOUTH OF THE FLORIDA PANHANDLE
NEAR 30N86W. A WARM FRONT EXTENDS SOUTHEASTWARD FROM THE LOW
ALONG 29N85W 26N83W. THIS FRONTAL BOUNDARY IS ACTUALLY FAIRLY
WELL DEFINED IN SFC OBS AND ON DOPPLER RADAR WHICH SHOWS THE
LEADING EDGE OF A LINE OF NUMEROUS SHOWERS AND TSTMS MOVING
ACROSS THE W COAST OF FLORIDA N OF 26N. SFC WINDS ARE GENERALLY
NEAR 10 KT FROM THE SW WITH LIGHT E-SE WINDS EAST OF THE
BOUNDARY. IN THE UPPER LEVELS...AN ELONGATED MID TO UPPER LEVEL
HIGH IS CENTERED OVER ERN WITH RIDGING EXTENDING TO NEAR 87W
ALONG 26N/27N. ANOTHER SMALLER MID/UPPER HIGH IS OVER THE FAR SE
GULF. UPPER DIFFLUENT AIR BETWEEN THESE FEATURES AND THE
WESTERLY FLOW OVER THE SRN UNITED STATES IS GENERATING A FAIR
AMOUNT OF UPPER LEVEL MOISTURE WITH EMBEDDED SCATTERED SHOWERS
IN THE NW GULF. SCATTERED MODERATE CONVECTION HAS FIRED IN THE
BAY OF CAMPECHE FROM 17N-22N BETWEEN 91W-95W ASSOCIATED WITH
UPPER DIFFLUENCE BETWEEN THE UPPER HIGHS AND AN UPPER LOW NEAR
20N94W. THE WEATHER PATTERN WILL BE CHANGING AS A COLD FRONT
PRESSES INTO N GULF LATE WED. GFS INDICATES THAT THIS FRONT WILL
LIKELY DIG TO NEAR 25N BEFORE BECOMING STATIONARY AND LIFTING
OUT.

THE CARIBBEAN SEA...
CONDITIONS REMAIN QUIET ACROSS THE CARIBBEAN TONIGHT WITH AN
ABUNDANT AMOUNT OF DRY STABLE UPPER LEVEL AIR NOTED ON WATER
VAPOR IMAGES W OF 76W. A FEW LEFT OVER PATCHES OF CLOUDS AND
ISOLATED SHOWERS FROM EARLIER TSTMS OVER CUBA ARE MOVING
SOUTHWARD DRIVEN BY NLY UPPER LEVEL FLOW BETWEEN AN ANTICYCLONE
OVER THE YUCATAN PENINSULA AND A LARGE UPPER LEVEL LOW IN THE E
CARIBBEAN. OTHERWISE...MID-HIGH LEVEL CLOUDINESS AND MAYBE SOME
ISOLATED SHOWERS LIE BETWEEN 64W AND 76W MOVING CYCLONICALLY
AROUND THE UPPER LOW. THE DEEPEST MOISTURE IN THE REGION IS IN
THE EXTREME SE CORNER WHERE NUMEROUS SHOWERS AND TSTMS ARE OVER
THE WINDWARD ISLANDS ASSOCIATED WITH A WELL DEFINED TROPICAL
WAVE ALONG 58W. THIS MOISTURE WILL CONTINUE TO SPREAD
EAST-NORTHEASTWARD ACROSS THE EASTERN CARIBBEAN TODAY. LIGHT TO
MODERATE TRADES NEAR 10-20 KT ARE OBSERVED IN THE REGION...THESE
WINDS ARE LIKELY TO REMAIN THAT WAY OVER THE NEXT COUPLE OF
DAYS.

THE ATLANTIC OCEAN...
A LARGE DEEP UPPER LEVEL TROUGH COVERS THE WRN ATLC AND THE
EASTERN CARIBBEAN. A TAIL SFC TROUGH/COLD FRONT EXTENDS FROM THE
EXTRATROPICAL STORM FLORENCE AND ENTERS THE AREA ALONG 32N60W
28N67W 24N74W TO THE FLORIDA STRAITS. THIS SFC TROUGH IS WELL
DEFINED IN OBSERVATIONS AND ON SATELLITE IMAGERY. A WEAK LOW
PRES AREA NOW APPEARS THAT IT MIGHT BE FORMING ALONG THE
BOUNDARY NEAR 27N70W. SCATTERED SHOWERS ARE WITHIN 120 NM OF THE
BOUNDARY. A LARGE FETCH OF N/NE WINDS PERSISTS OFF THE MID ATLC
AND NE US COAST BETWEEN EXTRATROPICAL FLORENCE AND THE 1023 MB
HIGH BUILDING INTO NEW ENGLAND. ASSOCIATED MODERATE TO STRONG NE
SWELL WILL CONTINUE TO PRODUCE DANGEROUS SURF CONDITIONS AT
BEACHES EXPOSED TO NE SWELL OVER THE NEXT COUPLE OF
DAYS...BEFORE SUBSIDING THROUGH THE WEEKEND. SEE STATEMENTS FROM
LOCAL WEATHER SERVICE OFFICES FOR MORE DETAILS. HURRICANE GORDON
IS MOVING NORTHWARD AROUND THE NW PERIPHERY OF A WEAK
SUB-TROPICAL RIDGE CENTERED NEAR 19N54W. THE MID TO UPPER LEVEL
RIDGING IN THE REGION HAS BEEN SIGNIFICANTLY ERODED EARLIER BY
FLORENCE AND NOW BY GORDON AND A LARGE UPPER LEVEL LOW
CENTERED NEAR 31N46W...WHICH IS MOVING NORTHWESTWARD. SCATTERED
SHOWERS ARE SPIRALING AROUND THE LOW FROM 27N-35N BETWEEN
40W-48W. BECAUSE OF THE LARGE BREAK IN THE SUBTROPICAL
RIDGE...GORDON IS IN RECURVATURE AND IS EXPECTED TO STAY IN THE
OPEN ATLANTIC. FARTHER EAST...A STRENGTHENING MID TO UPPER HIGH
IS OVER THE ERN ATLC OFF THE COAST OF AFRICA NEAR 25N28W. THIS
IS THE PRIMARY STEERING COMPONENT FOR TROPICAL DEPRESSION EIGHT
KEEPING THE SYSTEM ON A GENERAL WESTWARD TRACK OVER THE NEXT
COUPLE OF DAYS. ACCORDING TO THE CIMSS SAL TRACKING PRODUCT AND
THE MILKY APPEARANCE ON EARLY MORNING VIS IMAGES...A WIDESPREAD
AREA OF SAHARAN DUST HAS SPREAD TO NEAR 45W. THIS DUST IS LIKELY
TO BE AN INHIBITING FACTOR FOR GORDON. AT THE SFC...A 1026 MB
HIGH IS CENTERED SW OF THE AZORES NEAR 36N35W WITH RIDGING
DOMINATING THE E ATLC.

$$
CANGIALOSI





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