[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 241757
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU JUL 24 2008

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...

T.S. DOLLY IS DUMPING HEAVY RAINS AS IT MOVES FARTHER INLAND
OVER THE DEEP SOUTH AND THE NE PORTION OF MEXICO. AT 24/1800
UTC...IT IS LOCATED NEAR 27.9N 99.8W VERY NEAR THE U.S./MEXICO
BORDER...ABOUT 25 NM...50 KM NW OF LAREDO TEXAS. ESTIMATED
MINIMUM PRESSURE IS 998 MB. MAXIMUM SUSTAINED WIND SPEED IS 35
KT WITH HIGHER GUSTS. WEAKENING IS FORECAST DURING THE NEXT 24
HOURS. PLEASE SEE THE LATEST NHC FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC AND THE PUBLIC ADVISORY
UNDER MIATCPAT4/WTNT34 KNHC FOR MORE DETAILS. DOPPLER RADAR AND
SURFACE DATA INDICATE THAT DOLLY STILL HAS A LARGE CIRCULATION
ACCOMPANIED BY NUMEROUS CONVECTIVE BANDS. THE MOST PROMINENT
CONVECTION IS TO THE SOUTHEAST OF THE CENTER. DOLLY IS EXPECTED
TO PRODUCE TOTAL RAINFALL ACCUMULATIONS OF 8 TO 12 INCHES...WITH
ISOLATED AMOUNTS OF 20 INCHES...OVER PORTIONS OF SOUTH TEXAS AND
NORTHEASTERN MEXICO. THESE RAINS ARE VERY LIKELY TO CAUSE
WIDESPREAD FLOODING. ISOLATED TORNADOES ARE ALSO POSSIBLE OVER
SOUTH CENTRAL TEXAS THE REST OF TODAY.

...TROPICAL WAVES...

A HIGH AMPLITUDE TROPICAL WAVE IS ALONG 34W S OF 23N MOVING W
NEAR 20 KT. VIS SATELLITE IMAGERY INDICATES A BROAD CYCLONIC
CIRCULATION AND A 1012 MB LOW IS ADDED ALONG THE WAVE AXIS NEAR
14N. THIS LOW IS FORECAST BY THE COMPUTER MODELS TO MOVE WNW
DURING THE NEXT 24-48 HOURS. SHOWER ACTIVITY IS VERY LIMITED AT
THIS TIME AND SIGNIFICANT DEVELOPMENT OF THIS SYSTEM IS NOT
EXPECTED DURING THE NEXT COUPLE OF DAYS. THE WAVE SHOWS UP VERY
WELL ON THE MIMIC-TPW PRODUCT FROM CIMSS WHERE A LARGE BULGE OF
MOISTURE IS OBSERVED. IN ADDITION...THE 850 MB RELATIVE
VORTICITY ALSO SUPPORTS THE PRESENCE OF THIS SFC LOW. TIGHT PRES
GRADIENT BETWEEN THE LOW AND THE ATLC SFC HIGH WILL PRODUCE SOME
INCREASE IN WINDS ACROSS THE CENTRAL ATLC DURING THE UPCOMING
WEEKEND.

A TROPICAL WAVE IS ALONG 58W S OF 18N MOVING W NEAR 10 KT.
WEAK INVERTED-V CURVATURE IS OBSERVED ON SATELLITE IMAGERY. THE
WAVE IS BENEATH STRONG TO MODERATE SUBSIDENCE/DRY AIR ALOFT WITH
SCATTERED SHOWER ACTIVITY ACROSS GUYANA. LOW TOP SHOWERS ARE
ALSO OCCURRING NEAR THE NORTHERN END OF THE WAVE AXIS.

A TROPICAL WAVE IS OVER CENTRAL AMERICA ALONG 84W/85W S OF 17N
MOVING W NEAR 10 KT. CLUSTERS OF SCATTERED MODERATE/ISOLATED
STRONG CONVECTION ARE BEHIND THE WAVE AXIS AFFECTING THE SW
CARIBBEAN AND THE ATLC COAST OF NICARAGUA. A DIFFLUENT PATTERN
ALOFT OVER THE AREA IS ALSO ENHANCING THIS CONVECTIVE ACTIVITY.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 10N14W 11N25W 7N36W 5N46W 7N57W. A
LARGE CLUSTER OF MODERATE TO STRONG CONVECTION HAS MOVED OFF THE
AFRICAN COAST AND NOW COVERS THE AREA FROM 8N-12N BETWEEN
17W-21.5W. THIS CONVECTIVE ACTIVITY IS LIKELY ASSOCIATED WITH A
NEW TROPICAL WAVE. THE VERTICAL SOUNDING FROM DAKAR THIS MORNING
SHOWED NLY WINDS AT LOW LEVELS INDICATING THAT THE WAVE HAS NOT
CROSS THIS AREA YET. THE HOVMOLLER DIAGRAM DEPICTS THE WWD
PROPAGATION OF THIS AREA OF SHOWERS AND TSTMS OVER WESTERN
AFRICA AND COASTAL WATERS. WE WILL WAIT FOR FURTHER DATA BEFORE
PLACING THE WAVE AXIS. SCATTERED MODERATE CONVECTION IS WITHIN
120 NM N OF AXIS BETWEEN 35W-55W.

...DISCUSSION...

GULF OF MEXICO...
DOLLY...THE FOURTH TROPICAL CYCLONE OF THE 2008 HURRICANE SEASON
MADE LANDFALL YESTERDAY ON SOUTH PADRE ISLAND TEXAS. TODAY...IN
THE TROPICAL STORM STATUS CONTINUES TO DUMP HEAVY RAIN OVER
SOUTH TEXAS AND NE MEXICO...SO A SIGNIFICANT POTENTIAL FOR
INLAND FLOODING CONTINUES. SEE SPECIAL FEATURES ABOVE FOR MORE
DETAILS. BROAD UPPER LEVEL ANTICYCLONE ASSOCIATED WITH DOLLY
EXTENDS A RIDGE ACROSS THE ENTIRE GULF AND THE FLORIDA
PENINSULA. THIS IS AIDING IN GENERATING SCATTERED SHOWER WITH
EMBEDDED TSTMS ACROSS THE NE GULF WATERS NEAR THE FLORIDA BIG
BEND REGION. AS OF 1500Z...A SFC TROUGH IS ANALYZED ACROSS THIS
AREA AND GOES FROM 30N83W TO 25N85W. MAINLY HIGH CLOUDS ARE SEEN
OVER THE WESTERN GULF. AT THE SURFACE...THE ATLANTIC RIDGE
EXTENDS WESTWARD AND ENVELOPS THE ERN GULF WITH A WEAK 1019 MB
HIGH CENTERED NEAR 28N87W. LIGHT AND VARIABLE WINDS PREVAIL
UNDER THE INFLUENCE OF THIS SYSTEM. HIGH PRES WILL CONTINUE TO
BUILD OVER NRN GULF WATERS THROUGH SUN.

CARIBBEAN SEA...
UPPER-LEVEL NORTHERLY WINDS ASSOCIATED WITH DOLLY'S OUTFLOW
COVERS THE NW CARIBBEAN AND THE YUCATAN PENINSULA WHILE AN UPPER
TROUGH EXTENDS FROM THE W ATLC ALL THE WAY SOUTH INTO THE
CARIBBEAN TO THE GULF OF HONDURAS. THE REMAINDER OF THE BASIN IN
UNDER THE INFLUENCE OF AN UPPER-LEVEL RIDGE ANCHORED ON A HIGH
LOCATED JUST OVER PUERTO RICO. S-SW FLOW BETWEEN THE ABOVE
MENTIONED UPPER LEVEL FEATURES IS DRAWING SUFFICIENT UPPER LEVEL
MOISTURE FROM NRN SOUTH AMERICA INTO THE CARIBBEAN SEA ACROSS
JAMAICA AND EASTERN CUBA. HISPANIOLA. THESE WINDS ARE ALSO
ENHANCING CONVECTION OVER PANAMA AND THE SW CARIBBEAN. MODERATE
TO STRONG SUBSIDENCE DOMINATES THE E PORTION OF THE BASIN. A
TROPICAL WAVE IS MOVING WESTWARD ACROSS CENTRAL AMERICA. A
SECOND ONE IS APPROACHING THE LESSER ANTILLES AND WILL MOVE INTO
THE E CARIBBEAN TOMORROW. SEE TROPICAL WAVE SECTION FOR DETAILS.
MODERATE TO STRONG TRADE WINDS ARE ACROSS THE AREA WITH THE
STRONGEST WINDS JUST OFF THE COLOMBIAN COAST.

ATLANTIC OCEAN...
A 1030 MB HIGH LOCATED NEAR 36N54W DOMINATES ALMOST THE ENTIRE
FORECAST AREA. THIS SYSTEM WILL SLIGHTLY STRENGTHEN DURING THE
NEXT FEW DAYS PRODUCING MODERATE TO STRONG TRADE WINDS ACROSS
THE TROPICS. BROAD AREA OF UPPER TROUGHING COVERS THE WRN ATLC
AND EXTENDS S INTO THE WESTERN CARIBBEAN. A SFC TROUGH PERSISTS
OVER THE W-CENTRAL ATLC AND NOW EXTENDS ALONG 59W/60W N OF 22N.
VIS SATELLITE IMAGERY INDICATES THAT A SWIRL OF LOW LEVEL CLOUDS
REMAINS ASSOCIATED WITH THIS TROUGH NEAR 28N. LIGHTNING DATA
DEPICTS ISOLATED TSTMS NEAR THE NORTHERN END OF THE TROUGH. THE
REMAINDER OF THE ATLANTIC OCEAN IS DOMINATED BY BENIGN UPPER
LEVEL FEATURES WHERE STRONG SUBSIDENCE AND A DRY STABLE
ATMOSPHERE ARE IN PLACE...PARTICULARLY BETWEEN 40W-65W. A LARGE
AREA OF STRATOCUMULUS CLOUDS IS WRAPPING AROUND THE SFC LOW
ASSOCIATED WITH THE TROPICAL WAVE OVER THE FAR ERN ATLC.

$$
GR




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