[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 252355
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT TUE SEP 25 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
2315 UTC.

...SPECIAL FEATURES...

KAREN...THE ELEVENTH NAMED STORM OF THE 2007 HURRICANE SEASON
DEVELOPED THIS MORNING IN THE EASTERN ATLANTIC. AT 25/2100 UTC
THIS TROPICAL CYCLONE WAS NEAR 11.1N 39.9W OR ABOUT 1240 NM...
2305 KM...EAST OF THE WINDWARD ISLANDS...MOVING W-NW AT 13 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1005 MB. MAXIMUM SUSTAINED
WINDS ARE 35 KT WITH GUSTS TO 45 KT. SEE LATEST NHC FORECAST
ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC AND THE
PUBLIC ADVISORY UNDER MIATCPAT2/WTNT32 KNHC FOR MORE DETAILS.
KAREN CONTINUES TO SHOW SOME BANDING FEATURES AND A WELL-DEFINED
CIRCULATION ON VISIBLE IMAGES...BUT ITS PRESENTATION ON INFRARED
IMAGERY IS NOT VERY IMPRESSIVE. THE SYSTEM CONTINUES TO LACK
MUCH IN THE WAY OF CENTRAL DEEP CONVECTION AND...IN FACT...THE
OVERALL AMOUNT OF DEEP CONVECTION IS MINIMAL. THE UPPER-LEVEL
OUTFLOW OVER THE NORTHERN SEMICIRCLE HAS BECOME A LITTLE BETTER
ESTABLISHED AND...IF KAREN DEVELOPS SOME MORE CENTRAL CONVECTION
IT COULD STRENGTHEN SOME DURING THE NEXT COUPLE OF DAYS. THE
OFFICIAL NHC FORECAST KEEPS KAREN AS A TROPICAL STORM DURING THE
NEXT 5 DAYS.

DATA FROM THE AIR FORCE RECONNAISSANCE AIRCRAFT SHOWS THAT THE
AREA OF LOW PRESSURE IN THE SOUTHWESTERN GULF OF MEXICO HAS A
WELL-DEFINED CIRCULATION...AND IS UPGRADED TO A TROPICAL
DEPRESSION STATUS. AT 25/2215Z...TROPICAL DEPRESSION THIRTEEN
WAS NEAR 21.7N 95.0W OR ABOUT 165 NM...305 KM...EAST OF TAMPICO
MEXICO...MOVING TOWARD THE SW SLOWLY AT 3 KT. LITTLE OVERALL
MOTION IS EXPECTED OVER THE NEXT 24 HOURS. ESTIMATED MINIMUM
CENTRAL PRESSURE IS 1010 MB. MAXIMUM SUSTAINED WINDS ARE 25 KT
WITH GUSTS TO 35 KT. SEE LATEST NHC FORECAST ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC AND THE PUBLIC ADVISORY
UNDER MIATCPAT3/WTNT33 KNHC FOR MORE DETAILS. THERE IS STILL
SOME SOUTHWESTERLY SHEAR OVER THE CYCLONE ASSOCIATED WITH AN
UPPER LOW ALONG THE MEXICAN COAST NEAR TAMPICO. THIS SHEAR IS
EXPECTED TO RELAX AND BE REPLACED BY AN UPPER ANTICYCLONE OVER
THE NEXT COUPLE OF DAYS...WHICH WOULD ALLOW THE SYSTEM AN
OPPORTUNITY TO STRENGTHEN. AS A RESULT...THE DEPRESSION COULD
BECOME A TROPICAL STORM ON WEDNESDAY.

...TROPICAL WAVES...

A TROPICAL WAVE WAS ADDED TO THE 1800 UTC SURFACE MAP ALONG 19W
S OF 18N BASED ON SURFACE DATA...SATELLITE IMAGERY AND AN
EARLIER QUIKSCAT PASS THAT SHOWED THE WIND SHIFT ASSOCIATED WITH
THE WAVE AXIS. IN ADDITION...THE WAVE SHOWS UP WELL IN THE LOW
LEVEL SATELLITE DERIVED WINDS AND VORTICITY...AND THE UW CIMSS
TPW PRODUCTS. MOST OF THE STRONG CONVECTION IS AHEAD OF THE WAVE
AXIS...PROBABLY ASSOCIATED WITH A LOW EMBEDDED IN THE ITCZ.
SCATTERED SHOWERS ARE WITHIN 130 NM EITHER SIDE OF WAVE APEX.

A 1013 MB LOW PRESSURE AREA IS NEAR 17N63W ASSOCIATED WITH A
TROPICAL WAVE ALONG 63W SOUTH OF 21N. CONVECTION HAS DIMINISHED
NEAR THE LOW CENTER THIS EVENING. THE SYSTEM HAS CHANGED LITTLE
IN ORGANIZATION AND UPPER-LEVEL WINDS HAVE BECOME LESS FAVORABLE
FOR DEVELOPMENT. HOWEVER...THE LOW SHOULD MOVE TOWARD THE
NORTHWEST...BRINGING SQUALLY WEATHER TO THE NORTHERN LEEWARD
ISLANDS...THE UK/US VIRGIN ISLANDS AND PUERTO RICO DURING THE
NEXT DAY OR SO. INTERESTS IN THESE AREAS SHOULD CONTINUE TO
MONITOR THE PROGRESS OF THIS SYSTEM. SATELLITE IMAGERY DEPICTS
SCATTERED MODERATE CONVECTION MAINLY EAST OF THE WAVE AXIS FROM
17N-21N BETWEEN 58W-63W.

A WEAK TROPICAL WAVE IS ALONG 92W S OF 18N MOVING W 10-15 KT.
WAVE REMAINS DIFFICULT TO LOCATE WITH ITS POSITION BASED MAINLY
ON CONTINUITY FROM PREVIOUS ANALYSES. SCATTERED MODERATE
CONVECTION IS MOSTLY INLAND NEAR THE GUATEMALA/MEXICO BORDER.
FOR FUTURE INFO ON THIS WAVE PLEASE REFER TO PACIFIC DISCUSSION
UNDER MIATWDEP.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 8N16W 6N24W 12N34W 5N46W 5N57W.
CLUSTERS OF MODERATE TO ISOLATED STRONG CONVECTION ARE FROM
4N-8N BETWEEN 22W-28W.

DISCUSSION...

GULF OF MEXICO...
THE MAIN WEATHER FEATURE ACROSS THE GULF OF MEXICO IS NOW
TROPICAL DEPRESSION THIRTEEN LOCATED IN THE SW PORTION OF THE
AREA. SEE SPECIAL FEATURES ABOVE. A SURGE OF TROPICAL MOISTURE
IS OVER THE BASIN MAINLY WEST OF 90W FROM THE BAY OF CAMPECHE
ALL THE WAY NORTH TO LOUISIANA. UPPER DIFFLUENCE BETWEEN AN
UPPER LOW NEAR TAMPICO AND AN UPPER RIDGE THAT CONTINUES TO
DOMINATE MUCH OF THE CENTRAL GULF IS ENHANCING THIS SHOWER/TSTM
ACTIVITY. VERY DRY MID TO UPPER AIR IS BEING ADVECTED INTO THE
NE GULF AROUND AN UPPER TROUGH EXTENDING INTO THE AREA FROM THE
WRN ATLC...WHILE AN AREA OF DISTURBED WEATHER PERSISTS OVER
SOUTH FLORIDA...WEST-CENTRAL CUBA AND THE WESTERN BAHAMAS. THIS
ACTIVITY IS PRIMARILY ASSOCIATED WITH A MID TO UPPER LEVEL
TROUGH. SURFACES PRESSURES ARE NOT FALLING AT THIS TIME AND
ADDITIONAL DEVELOPMENT...IF ANY WILL BE SLOW TO OCCUR. THIS
SYSTEM COULD BRING LOCALLY HEAVY RAINS TO SOUTH FLORIDA AND THE
KEYS DURING THE NEXT DAY OR TWO. AS OF 2100 UTC...A SFC TROUGH
IS ANALYZED OVER THE AREA AND RUNS FROM 27N79W TO 23N83W.
ELSEWHERE AT THE SFC...RIDGING EXTENDS INTO THE NE GULF AND SE
U.S. AROUND A 1024 MB HIGH PRES CENTERED OVER THE W ATLC NEAR
37N70W. RIDGING WILL PERSIST OVER THE NRN GULF THROUGH WED WHILE
LOW PRES MEANDERS IN THE SW PORTION. A WEAK COLD FRONT IS
FORECAST TO MOVE OVER THE NORTHERN GULF WATERS THU NIGHT.

CARIBBEAN SEA...
THE MAIN WEATHER FEATURE IN THE CARIBBEAN IS ASSOCIATED WITH THE
TROPICAL WAVE AND ASSOCIATED LOW PRESSURE AREA MOVING TOWARD THE
NW. SEE TROPICAL WAVE SECTION. OTHERWISE THE BASIN IS FAIRLY
TRANQUIL. AN UPPER RIDGE/TROUGH/RIDGE PATTERN CONTINUES TO
DOMINATE THE AREA. CONVECTION HAS FLARED UP OVER DOMINICAN
REPUBLIC AND ALONG THE COAST OF VENEZUELA THIS EVENING. THIS
ACTIVITY SEEMS MOSTLY ASSOCIATED WITH DIFFLUENT FLOW ALOFT OVER
THE AREA. UPPER SLY FLOW AHEAD OF AN UPPER TROUGH IS ADVECTING
HIGH CLOUDS/MOISTURE NEWD OVER THE CENTRAL CARIBBEAN. THE
COLOMBIAN LOW IS NEAR 10N67W GENERATING SOME SHOWER ACTIVITY.
TRADES REMAIN LIGHT TO MODERATE ACROSS THE BASIN...BUT
WINDS/SEAS COULD BE HIGHER AT TIMES IN SQUALLS NEAR THE LOW/WAVE
MOVING THROUGH THE EASTERN CARIBBEAN.

ATLANTIC OCEAN...
AN AREA OF DISTURBED WEATHER PERSISTS OVER SOUTH FLORIDA...
WEST-CENTRAL CUBA AND THE WESTERN BAHAMAS. A CLOSED UPPER LOW
OVER THE FLORIDA PENINSULA AND A SFC TROUGH THAT HAS DEVELOPED
OVER SOUTH FLORIDA ARE CREATING THIS HUMID AND UNSTABLE WEATHER
PATTERN. MORE DETAILS IN THE GULF OF MEXICO SECTION. ELSEWHERE
AT THE SFC... A 1024 MB HIGH LOCATED N OF THE AREA IS PRODUCING
AN ELY FLOW OVER THE W ATLC. A WEAK SFC TROUGH ENTERS THE
FORECAST REGION NEAR 31N38W...THEN CONTINUES ALONG 28N50W TO
23N64W. SCATTERED SHOWERS ARE WITHIN 90 NM AHEAD OF THE TROUGH
AXIS. ANOTHER WEAK TROUGH IS ALONG 52W WITH LIMITED SHOWER
ACTIVITY.  MODERATE RIDGING TAKES OVER IN THE E ATLC. THIS
PATTERN IS STILL PRODUCING MODERATE TRADES IN THE E ATLC...
EXCEPT STRONGER NEAR THE NW COAST OF AFRICA WHERE THE PRES
GRADIENT TIGHTENS.

IN THE MID AND UPPER LEVELS...A BROAD UPPER TROUGH EXTENDS
MAINLY EAST TO WEST ALONG 29N/30N WEST OF 40W TO THE UPPER LOW
LOCATED OVER FLORIDA. THIS TROUGH IS SUPPORTING THE SFC TROUGH
MENTIONED ABOVE AND A COLD FRONT THAT IS CLIPPING THE AREA
BETWEEN 50W-60W. ABUNDANT MID/TO UPPER LEVEL MOISTURE IS JUST
SOUTH OF THE TROUGH AXIS. AN AMPLIFIED UPPER RIDGE IS SEEN
E OF THE TROUGHING EXTENDING NE FROM AN UPPER HIGH SITUATED NEAR
21N38W TO BEYOND 32N33W. A LARGE UPPER LOW IS LOCATED E OF THE
RIDGE BETWEEN THE MADEIRA/CANARY ISLANDS NEAR 31N19W. ISOLATED
SHOWERS AREA NEAR THE LOW CENTER AND OVER THE CANARY ISLANDS.

$$
GR




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