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