[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 272349
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU SEP 27 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...

TROPICAL STORM KAREN HAS WEAKENED SLIGHTLY BUT STILL A TROPICAL
STORM OVER THE OPEN WATERS OF THE CENTRAL ATLANTIC. AT 27/2100
UTC KAREN WAS NEAR 14.3N 48.5W OR ABOUT 735 NM EAST OF THE
WINDWARD ISLANDS...MOVING WEST NORTHWEST NEAR 11 KT. ESTIMATED
MINIMUM CENTRAL PRESSURE IS 1005 MB. MAXIMUM SUSTAINED WINDS ARE
50 KT WITH GUSTS TO 60 KT. SEE LATEST NHC FORECAST ADVISORY
UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC AND THE PUBLIC
ADVISORY UNDER MIATCPAT2/WTNT32 KNHC FOR MORE DETAILS. MODERATE
TO STRONG SOUTHWESTERLY SHEAR AHEAD OF A MID-OCEANIC TROUGH IS
AFFECTING KAREN AND THIS SHEAR IS EXPECTED TO PERSIST OVER THE
NEXT FEW DAYS. THUS...A GRADUAL WEAKENING IS FORECAST. LATEST
SATELLITE IMAGERY SHOWS THAT KAREN'S CENTER IS CLOSE TO THE DEEP
CONVECTION. MODERATE TO STRONG CONVECTION IS FROM 14N-17N
BETWEEN 46W-50W. A BAND OF SCATTERED MODERATE TO ISOLATED STRONG
CONVECTION IS WITHIN 300 NM EAST OF CENTER FROM 11N-17N.

TROPICAL DEPRESSION THIRTEEN WAS UPGRADED TO TROPICAL STORM
LORENZO AT 1800 UTC...THE TWELFTH NAMED STORM OF THE 2007
HURRICANE SEASON. REPORTS FROM AN AIR FORCE PLANE INVESTIGATING
LORENZO INDICATE THAT THE WINDS HAVE BEEN INCREASING AND THE
PRESSURE HAS COME DOWN TO AT LEAST 999 MB. SOME ADDITIONAL
STRENGTHENING IS FORECAST AND LORENZO COULD REACH THE MEXICAN
COAST AS A HURRICANE BECAUSE THE SHEAR IS LOW AND THE OCEAN IS
WARM. AT 27/2100 UTC IT WAS NEAR 20.4N 95.9W OR ABOUT 90
NM...170 KM...EAST-SOUTHEAST OF TUXPAN MEXICO...MOVING WEST NEAR
4 KT...AND THIS GENERAL MOTION TOWARD THE COAST OF MEXICO IS
EXPECTED UNTIL THE CENTER CROSSES THIS COAST IN ABOUT 12 HOURS
OR SO. SEE LATEST NHC FORECAST ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT3/WTNT23 KNHC AND THE PUBLIC ADVISORY UNDER MIATCPAT3/
WTNT33 KNHC FOR MORE DETAILS. WATCHES AND WARNINGS HAVE BEEN
ISSUED. LORENZO IS EXPECTED TO PRODUCE TOTAL RAINFALL
ACCUMULATIONS OF 5 TO 10 INCHES OVER THE MEXICAN STATE OF
VERACRUZ...WITH POSSIBLE ISOLATED MAXIMUM AMOUNTS OF 15 INCHES.
VERACRUZ WAS REPORTING STEADY LIGHT RAIN DURING THE LAST SEVERAL
HOURS AND POZA RICA HEAVY RAIN AT TIMES. NUMEROUS MODERATE TO
SCATTERED STRONG CONVECTION IS WITHIN 100 NM OF 20N95W.

...TROPICAL WAVES...

A TROPICAL WAVE IS OVER THE E ATLC ALONG 26W SOUTH OF 19W MOVING
W 10-15 KT. THE WAVE SHOWS UP WELL IN LOW LEVEL SATELLITE
DERIVED WINDS AND VORTICITY...AND THE UW CIMSS TPW PRODUCTS WITH
A GOOD MOISTURE SURGE. SHOWERS AND THUNDERSTORMS ASSOCIATED WITH
THE WAVE HAVE DECREASED...AND SIGNIFICANT DEVELOPMENT OF THIS
SYSTEM IS NOT ANTICIPATED. WIDELY SCATTERED MODERATE CONVECTION
IS WITHIN 90 NM EITHER SIDE OF AXIS...MAINLY FROM 10N-14N.

A TROPICAL WAVE IS OVER THE CARIBBEAN ALONG 74W S OF 21N MOVING
W NEAR 15 KT. THIS WAVE IS PRODUCING DISORGANIZED CLOUDINESS AND
SHOWERS FROM THE CENTRAL CARIBBEAN SEA NORTHWARD ACROSS
HISPANIOLA...THE SOUTHEASTERN BAHAMAS...AND THE ADJACENT
ATLANTIC. DEVELOPMENT IS NOT EXPECTED. A CLUSTER OF MODERATE TO
ISOLATED STRONG CONVECTION HAS DEVELOPED OVER HISPANIOLA...JUST
BEHIND THE WAVE AXIS. SIMILAR CONVECTION IS SEEN ON THE SOUTH
END OF THE WAVE OVER WESTERN VENEZUELA AND NORTHERN COLOMBIA.
THIS CONVECTIVE ACTIVITY IS BEEN ENHANCING BY UPPER DIFFLUENT.
MOISTURE ASSOCIATED WITH THIS WAVE IS FORECAST TO SPREAD OVER
EASTERN CUBA AND JAMAICA TOMORROW.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 7N12W 10N24W 8N35W 12N42W 8N60W.
BESIDES FOR THE ACTIVITY ASSOCIATED WITH T.S. KAREN AND THE
TROPICAL WAVE OVER THE E ATLC...SCATTERED MODERATE TO ISOLATED
STRONG CONVECTION IS NEAR THE COAST OF AFRICA FROM 11N-14N
BETWEEN 12W-16W.

DISCUSSION...

GULF OF MEXICO...
TROPICAL STORM LORENZO...WHICH IS FORECAST TO IMPACT MEXICO
THIS FRIDAY IS THE MAIN WEATHER FEATURE ACROSS THE GULF OF
MEXICO. THE SLOW MOTION OF LORENZO WILL LIKELY PRODUCE
TORRENTIAL RAINFALL ALONG ITS PATH. SEE SPECIAL FEATURES ABOVE
FOR MORE DETAILS. AN UPPER RIDGE ANCHORED ON A HIGH OVER NE
MEXICO DOMINATES MUCH OF THE REGION...INCLUDING THE YUCATAN
PENINSULA. DRIER AIR IS FILTERING INTO THE E GULF IN WAKE OF THE
DEEP LAYER TROUGHING OVER THE FLORIDA PENINSULA. IN FACT...
BESIDES FOR LORENZO IN THE FAR SW PORTION...THE GULF IS PRETTY
TRANQUIL WITH A WEAK SFC PRES GRADIENT N OF 23N. UPPER
DIFFLUENCE BETWEEN THE AFOREMENTIONED RIDGE AND A DEEP LAYERED
UPPER-LEVEL TROUGH MOVING E OVER THE EASTERN U.S. IS HELPING TO
INDUCE SCATTERED SHOWERS AND ISOLATED TSTMS OVER THE NORTHERN
GULF WATERS JUST SOUTH OF THE LOUISIANA COAST.

CARIBBEAN SEA...
A TROPICAL WAVE IS MOVING WWD ACROSS THE CENTRAL CARIBBEAN. SEE
TROPICAL WAVE SECTION. SCATTERED SHOWERS AND TSTMS ARE OVER
PANAMA AND COSTA RICA DUE TO THE ITCZ. AN UPPER-LEVEL LOW HAS
DEVELOPED OVER WESTERN CUBA ALONG THE UPPER-LEVEL TROUGH THAT
CROSSES THE FLORIDA PENINSULA AND THE NW CARIBBEAN. UPPER
DIFFLUENCE BETWEEN THIS LOW/TROUGH AND AN UPPER RIDGE OVER THE
CENTRAL CARIBBEAN...JUST SOUTH OF HISPANIOLA IS SUPPORTING THE
SHOWERS AND TSTMS OVER EAST-CENTRAL CUBA. SIMILAR ACTIVITY IS
OVER NORTHERN CENTRAL AMERICA NEAR THE BASE OF THE TROUGH. TRADE
WINDS REMAIN LIGHT TO MODERATE ACROSS THE BASIN...BUT WINDS/SEAS
COULD BE HIGHER AT TIMES NEAR SQUALLS ASSOCIATED WITH THE
TROPICAL WAVE. NWLY UPPER WINDS ASSOCIATED WITH AN UPPER LOW
LOCATED OVER THE CENTRAL ATLC ARE ADVECTING HIGH CLOUDS/MID TO
UPPER LEVEL MOISTURE OVER PUERTO RICO AND THE NE CARIBBEAN INTO
THE LESSER ANTILLES.

ATLANTIC OCEAN...
A TROUGH OF LOW PRESSURE EXTENDING FROM JUST OFFSHORE THE EAST
COAST OF FLORIDA NORTH-NORTHEASTWARD ACROSS THE ATLANTIC FOR
SEVERAL HUNDRED MILES IS PRODUCING DISORGANIZED CLOUDINESS AND
THUNDERSTORMS OVER THE WESTERN ATLC AND THE BAHAMAS WEST OF 70W.
LIGHTNING DATA DEPICTS MOST OF THE TSTM ACTIVITY WITHIN 300 NM
EAST OF THE TROUGH AXIS. A 1010 MB SFC LOW IS ANALYZED ALONG THE
TROUGH AXIS NEAR 29N78W. THIS SYSTEM HAS BECOME LESS ORGANIZED
DURING THE DAY AND SIGNIFICANT DEVELOPMENT OF THIS DISTURBANCE
IS NOT EXPECTED BEFORE IT BECOMES ABSORBED BY A FRONTAL SYSTEM
IN THE NEXT COUPLE OF DAYS. UPPER FLOW REMAINS VERY DIFLUENT
OVER THIS AREA BETWEEN TROUGHING THROUGH FLORIDA AND RIDGING
EXTENDING N FROM THE CARIBBEAN ALONG 70W. AN UPPER LOW OVER THE
CENTRAL ATLC NEAR 22N56W IS GENERATING SOME SHOWER ACTIVITY. A
SFC TROUGH WAS ANALYZED OVER THIS AREA DURING THE PREVIOUS DAYS.
MODERATE SFC RIDGING REMAINS ANCHORED OVER THE E ATLC...
PRODUCING LIGHT TO MODERATE NE TRADES E OF 30W. THE UPPER LOW
THAT HAS BEEN AFFECTING THE FAR NE PORTION OF THE DISCUSSION
AREA IS MOVING NE APPROACHING PORTUGAL. AN UPPER RIDGE DOMINATES
THE TROPICAL ATLC WITH AN UPPER HIGH NEAR 12N35W.

$$
GR




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