[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 192355
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN AUG 19 2007

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN
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...METEOROLOGICAL ANALYSIS...
WEATHER OBSERVATIONS...AND RADAR.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2330 UTC.

...SPECIAL FEATURE...
AS OF 20/0000 UTC THE EYE OF EXTREMELY DANGEROUS HURRICANE DEAN
WAS LOCATED NEAR LATITUDE 17.5 NORTH...LONGITUDE 77.8 WEST OR
ABOUT 70 MILES...115 KM...WEST-SOUTHWEST OF KINGSTON JAMAICA AND
ABOUT 265 MILES...425 KM...EAST-SOUTHEAST OF GRAND CAYMAN. DEAN
IS MOVING TOWARD THE WEST NEAR 20 MPH...32 KM/HR. A MOTION
BETWEEN WEST AND WEST-NORTHWEST IS EXPECTED OVER THE NEXT 24
HOURS. ON THE FORECAST TRACK...THE CENTER OF DEAN WILL BE
PASSING VERY NEAR THE SOUTHWESTERN COAST OF JAMAICA DURING THE
NEXT SEVERAL HOURS...AND JUST SOUTH OF THE CAYMAN ISLANDS ON
MONDAY. MAXIMUM SUSTAINED WINDS REMAIN NEAR 125 KT WITH GUSTS TO
155 KT...THIS MAKES DEAN A STRONG CATEGORY FOUR HURRICANE. THE
ESTIMATED MINIMUM CENTRAL PRESSURE WAS 930 MB. FLUCTUATIONS IN
INTENSITY ARE COMMON IN MAJOR HURRICANES AND ARE POSSIBLE DURING
THE NEXT 24 HOURS.  DEAN HAS THE POTENTIAL TO BECOME A CATEGORY
FIVE HURRICANE IN THE NORTHWESTERN CARIBBEAN SEA ON MONDAY
...LIKE GILBERT IN 1988 AND WILMA IN 2005. ALL INTERESTS IN THE
WESTERN CARIBBEAN SEA...AND THE GULF OF MEXICO SHOULD CLOSELY
MONITOR THE PROGRESS OF THIS POWERFUL HURRICANE. PLEASE SEE THE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT4/WTNT24 KNHC AND THE LATEST PUBLIC ADVISORY UNDER
MIATCPAT4/WTNT34 KNHC FOR THE MOST RECENT WATCH AND WARNING
INFORMATION. FOR STORM INFORMATION SPECIFIC TO YOUR
AREA...INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE
MONITOR PRODUCTS ISSUED BY YOUR LOCAL WEATHER OFFICE. KINGSTON
JAMAICA REPORTED SUSTAINED WINDS OF 70 KT AT 21Z IN THE NE
EYEWALL. THE SATELLITE APPEARANCE OF DEAN REMAINS VERY
IMPRESSIVE WITH GOOD SYMMETRY TO IT'S EYE...EYEWALL...SPIRAL
RAINBANDS AND OUTFLOW. NUMEROUS MODERATE TO STRONG CONVECTION IS
WITHIN 90 NM OF THE CENTER. OUTER BANDS OF DEAN SPREAD MUCH
FARTHER AND ROUGHLY COVER THE REGION FROM 15N-21N BETWEEN
71W-80W.

...TROPICAL WAVES...

LARGE TROPICAL WAVE IS TILTED ALONG 23N50W 5N55W MOVING W NEAR
20 KT OVER THE PAST 24 HOURS. THE ASSOCIATED SFC CYCLONIC
TURNING SHOWS UP NICELY IN THE SURROUNDING BUOY/SHIP DATA. A
1009 MB LOW IS ALONG THIS WAVE NEAR 12N54W. THE LOW IS RATHER
WEAK AT THE MOMENT WITH THE CENTER PARTIALLY EXPOSED TO THE NE
OF AN AREA OF DENSER CLOUDS. DEVELOPMENT...ASSOCIATED WITH THIS
SMALL LOW...APPEARS UNLIKELY. THE REMAINDER OF THE AXIS IS
EMBEDDED WITHIN A LARGE CYCLONIC GYRE. THE NRN PORTION OF THE
WAVE IS THE ACTIVE REGION...IN TERMS OF CONVECTION...WITH IR
IMAGERY AND LIGHTNING DATA SHOWING SCATTERED SHOWERS AND TSTMS
FROM 18N-23N BETWEEN 48W-55W. THIS ACTIVITY IS BEING ENHANCED BY
AN ELONGATED UPPER TROUGH. THIS PORTION OF THE WAVE WILL
CONTINUE TO BE MONITORED AS SLOW DEVELOPMENT APPEARS POSSIBLE AS
IT TRACKS WNW OVER THE NEXT COUPLE OF DAYS.

THE NRN PORTION OF A TROPICAL WAVE ALONG 91W/92W EXTENDS INTO
THE BAY OF CAMPECHE S OF 21N MOVING W 10-15 KT. VIS IMAGES SHOW
A WEAK AREA OF CYCLONIC TURNING EVIDENT ALONG THE S PORTION OF
THE WAVE OVER THE EPAC WATERS. THE INTERACTION BETWEEN THIS WAVE
AND AN UPPER LOW IN THE MID-GULF IS PRODUCING SCATTERED SHOWERS
AND TSTMS OVER THE YUCATAN PENINSULA AND OVER THE CENTRAL GULF
WATERS...SEE GULF DISCUSSION BELOW FOR MORE DETAILS.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 12N15W 7N27W 14N49W 9N61W. ISOLATED
MODERATE CONVECTION IS WITHIN 120 NM S OF THE AXIS BETWEEN
24W-29W. SCATTERED MODERATE IS FROM 9N-11N BETWEEN 43W-47W.

DISCUSSION...

THE GULF OF MEXICO...
AN UPPER LOW CONTINUES TO PUSH W ACROSS THE GULF CENTERED NEAR
25N91W. AS WAS WELL PREDICTED BY MANY OF THE MODELS...THIS UPPER
CIRCULATION HAS BEEN MOVING W 15-20 KT WHICH IS LIMITING IT'S
IMPACTS ON DEAN. INSTABILITY NEAR THIS UPPER LOW ALONG WITH SOME
INTERACTION WITH A TROPICAL WAVE IN THE BAY OF CAMPECHE IS
PRODUCING SCATTERED SHOWERS AND TSTMS ACROSS THE CENTRAL GULF
FROM 22N-29N BETWEEN 87W-95W...AS INDICATED BY LIGHTNING DATA.
AT THE SFC...THE WRN EXTENT OF AN ATLC SUBTROPICAL RIDGE
CONTINUES TO HOLD IT'S PLACE ACROSS THE GULF. THIS IS ALLOWING
WINDS TO BE FAIRLY LIGHT OUT OF THE E TO SE ACROSS THE AREA.
HOWEVER...THIS WILL NOT BE THE CASE FOR LONG AS POWERFUL DEAN
TRACKS TOWARD THE SW PORTION OF THE AREA. SEE SPECIAL FEATURE
SECTION FOR DETAILS.

THE CARIBBEAN SEA...
ATTENTION REMAINS FOCUSED ON POWERFUL CATEGORY FOUR HURRICANE
DEAN. DEAN WILL CONTINUE TO HAVE SIGNIFICANT IMPACTS ON THE
CENTRAL AND WESTERN CARIBBEAN AS WELL AS THE YUCATAN PENINSULA
THROUGH TUE NIGHT. KINGSTON JAMAICA RECENTLY REPORTED 70 KT
SUSTAINED WINDS AT 21Z. FOR DETAILS REFER TO THE SPECIAL FEATURE
ABOVE. A CURIOUS FEATURE IS A NARROW SQUALL/FEEDER LINE WELL
AHEAD OF THE HURRICANE'S CENTER...PRESSING W ACROSS THE NW
CARIB.

THE ATLANTIC OCEAN...
A STRONG MID LEVEL RIDGE IS PARKED ACROSS THE WRN ATLC NEAR
31N76W. THIS IS THE FEATURE STEERING DEAN FAIRLY QUICKLY TO THE
W OR WNW ACROSS THE WESTERN CARIBBEAN. DEAN'S STRONG CIRCULATION
IS CAUSING DISTINCT SINKING/DRYING BEYOND IT'S OUTFLOW ACROSS
THE CENTRAL BAHAMAS AND REGIONS FURTHER N. ELY WINDS ARE QUITE
STRONG...25 TO 30 KT WITH HIGHER GUSTS ACROSS THE EXTREME SW
ATLC NEAR DEAN. THESE WINDS ARE DRIVING SOME SHOWER/TSTMS
STREAMERS ACROSS THE BAHAMAS AND S FLORIDA. FURTHER E...A LARGE
TROPICAL WAVE IN THE CENTRAL ATLC LOOKS MORE INTERESTING THIS
EVENING. FOR DETAILS REFER TO THE TROPICAL WAVES SECTION ABOVE.
AN UPPER LOW/ELONGATED TROUGH RUNS N-S ALONG 57W...ANOTHER UPPER
LOW IS CENTERED NEAR 31N30W. RIDGING DOMINATES THE REGION TO THE
S AND E OF THE UPPER LOWS EXTENDING FROM AN ANTICYCLONE OVER
AFRICA NEAR 24N7W.

AT THE SFC...A LARGE SCALE RIDGE DOMINATES THE ATLANTIC
DISCUSSION AREA ANCHORED BY A 1032 MB HIGH NEAR THE AZORES. THIS
IS AIDING IN THE WIDESPREAD FAIR WEATHER AND PRODUCING MODERATE
TRADES...EXCEPT STRONGER WINDS NEAR DEAN (AS DISCUSSED ABOVE)
AND NEAR THE LARGE TROPICAL WAVE.

$$
CANGIALOSI


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