[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 212355
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI SEP 21 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 FEATURE...

TROPICAL DEPRESSION TEN IS ALMOST ONSHORE NEAR 30.4N 86.7W NEAR
FORT WALTON BEACH FLORIDA. THE TROPICAL STORM WARNING FOR THE
GULF COAST HAS BEEN DISCONTINUED. THE DEPRESSION IS MOVING NW
NEAR 8 KT. THIS MOTION IS EXPECTED TO CONTINUE TONIGHT
...BRINGING THE CENTER OF THE DEPRESSION FARTHER INLAND. THE
LATEST MINIMUM CENTRAL PRESSURE REPORTED BY AN AIR FORCE RESERVE
UNIT RECONNAISSANCE AIRCRAFT WAS 1005 MB. RADAR AND SURFACE
OBSERVATIONS INDICATE THAT THE DEPRESSION HAS NOT STRENGTHENED
AND MAXIMUM SUSTAINED WINDS REMAIN NEAR 30 KT WITH GUSTS TO 40
KT IN A FEW SQUALLS.  A GRADUAL WEAKENING SHOULD BEGIN TONIGHT
AFTER THE CENTER MOVES FARTHER INLAND. PLEASE REFER TO THE
LATEST NHC FORECAST ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT5/WTNT25 KNHC AND THE PUBLIC ADVISORY UNDER
MIATCPAT5/WTNT35 KNHC FOR MORE DETAILS. RADAR IMAGERY SHOWS
BROKEN BANDS OF SCATTERED SHOWERS AND TSTMS ROTATING AROUND THE
DEPRESSION. SOME OF THIS ACTIVITY HAS SPREAD WELL INLAND THROUGH
THE FLORIDA PANHANDLE...SW GEORGIA AND SE ALABAMA. ISOLATED
TORNADOES ARE POSSIBLE ACROSS THESE AREAS THROUGH TONIGHT. IN
ADDITION TO THIS THREAT...RIP CURRENTS AND ROUGH SURF ARE A
CONCERN FOR PORTIONS OF THE GULF COAST. SEE STATEMENTS FROM
LOCAL WEATHER SERVICE OFFICES FOR MORE DETAILS.

...TROPICAL WAVES...

A TROPICAL WAVE HAS MOVED W OF THE CAPE VERDE ISLANDS TITLED
NW-SE ALONG 19N28W 6N25W MOVING W 10-15 KT. THIS ELONGATED AREA
OF CYCLONIC TURNING IS EASILY SEEN ON SATELLITE IMAGERY AND
DERIVED WINDS. THE WAVE ALSO SHOWS UP NICELY ON THE MIMIC TPW
ANIMATION AS A LARGE MOISTENED AREA WITH THE CREST REACHING WELL
INTO THE SUBTROPICS. WHILE THE SIGNATURE AND STRUCTURE IS
DEFINED ...CONVECTION IS NON-EXISTENT LIKELY SUPPRESSED BY THE
STABLE AIR SURROUNDING THIS FEATURE.

A LOWER LATITUDE TROPICAL WAVE IS ALONG 38W S OF 15N MOVING W 10
KT. MUCH OF THE WAVE ENERGY HAS BEEN ABSORBED WITHIN THE ITCZ.
THIS HAS MADE THE POSITION DIFFICULT TO PIN POINT WITH THE
CURRENT AXIS DRAWN THROUGH THE VERY BROAD FAINT INVERTED V-SHAPE
WITHIN THE ITCZ. ASSOCIATED SHOWERS AND TSTMS HAVE BECOME
INCREASINGLY DIFFUSE SPREAD OUT BY THE MODERATE TO STRONG
DIVERGENT MID TO UPPER FLOW IN THE AREA. SCATTERED MODERATE
CONVECTION IS FROM 9N-12N BETWEEN 36W-44W.

A WEAK TROPICAL WAVE IS OVER THE CENTRAL CARIBBEAN ALONG 71W S
OF 18N MOVING W 15-20 KT. THE NRN PORTION OF THE WAVE LIES
UNDERNEATH AN UPPER LOW BUT THIS INTERACTION IS ONLY PRODUCING
PATCHY CLOUDINESS AT THE MOMENT. THIS SHALLOW WAVE IS ONLY SEEN
ON THE MIMIC TPW ANIMATION WHICH DEPICTS A NARROW MODEST
MOISTURE SURGE MOVING THROUGH THE ABC ISLANDS. THIS ANIMATION
ALSO VERY WELL REVEALS HOW THIS ONCE LARGE WAVE SPLIT JUST E OF
60W WITH THE NRN PORTION...WHICH CONSUMED MOST OF THE
ENERGY...STILL LAGGING BEHIND E OF THE LESSER ANTILLES. MORE ON
THAT FEATURE IN THE ATLC DISCUSSION SECTION.

...THE ITCZ...
AXIS IS CENTERED ALONG 8N13W 10N24W 8N31W 10N41W 5N53W. BESIDES
FOR THE ACTIVITY ASSOCIATED WITH THE TROPICAL WAVE APPROACHING
40W...SCATTERED SHOWERS AND TSTMS ARE FROM 9N-13N BETWEEN
42W-51W.

DISCUSSION...

GULF OF MEXICO...
TROPICAL DEPRESSION TEN IS THE AREA OF FOCUS THIS EVENING IN THE
NE GULF. FOR DETAILS AND REFERENCES REFER TO THE SPECIAL FEATURE
SECTION ABOVE. SFC OBSERVATIONS AND SATELLITE IMAGERY SHOW A
WELL DEFINED TRAILING TROUGH AXIS WHICH EXTENDS SW FROM THE
DEPRESSION TO 24N90W. IR IMAGERY AND LIGHTNING DATA SUGGEST THAT
SCATTERED SHOWERS AND TSTMS ARE LOCATED WITHIN 60 NM OF THAT
BOUNDARY. VERY DRY AIR IN THE MID AND UPPER LEVELS SURROUNDS THE
DEPRESSION COVERING THE BULK OF THE W GULF. THE DRY SLOT NARROWS
TO THE E OF THE DEPRESSION BUT STILL REMAINS DISTINCT ON WATER
VAPOR IMAGERY. ABUNDANT DEEP MOISTURE IS POURING IN THE EXTREME
SE GULF. THIS MOISTURE IS BEING DRAWN NNE BY EXTENSIVE DEEP
LAYER SLY FLOW. DOPPLER RADAR AND LIGHTNING DATA INDICATE QUITE
A BIT OF TSTM ACTIVITY EMBEDDED IN THE AREA S OF 25N E OF 85W.
SFC REPORTS SHOW SOME GUSTY WINDS IN THIS ACTIVITY. SEVERAL
STATIONS IN THE FLORIDA KEYS ARE REPORTING GUSTS NEAR OR
SLIGHTLY ABOVE 30 KT. THIS MOISTURE WILL LIKELY EXPAND NWD
THROUGH TOMORROW AND THEN POSSIBLY NWWD.

CARIBBEAN SEA...
A LARGE AREA OF DISORGANIZED SCATTERED MODERATE CONVECTION
PERSISTS ACROSS THE CARIBBEAN GENERALLY W OF 76W. VISIBLE
IMAGERY SHOWS SOME SPIN TO THE CLOUDS NEAR 17N81W...THOUGH THIS
IS LIKELY MID-LEVEL WHEN COMPARED TO THE SFC OBSERVATIONS IN THE
REGION. THERE DOES APPEAR TO BE A SFC BOUNDARY BUT THIS IS
ANALYZED TO THE W OF THE MID-LEVEL VORTICITY ALONG 86W/87W FROM
13N-21N... AND THERE IS LOW CONFIDENCE IN THIS POSITION. A LARGE
CONTRIBUTING COMPONENT IS IN THE UPPER LEVELS. EXTENSIVE SWLY
FLOW AND DIFFLUENCE ALOFT BETWEEN THE DEPRESSION AND AN UPPER
HIGH OVER NICARAGUA IS LIKELY RESPONSIBLE FOR SOME OF THE
STRONGEST ACTIVITY WHICH CURRENTLY IS OVER CUBA. A FEW MODELS
SHOW SOME DEVELOPMENT IN THIS REGION OVER THE NEXT COUPLE OF
DAYS. HOWEVER...AT THE MOMENT THERE ARE NO SIGNS OF ORGANIZATION
AND SURFACES PRESSURES ARE NOT FALLING SO ADDITIONAL
DEVELOPMENT...IF ANY...IS EXPECTED TO BE SLOW TO OCCUR. THE
WEATHER ACROSS THE REMAINDER OF THE REGION IS FAIRLY TRANQUIL.
AN UPPER LOW IS SPINNING OVER HISPANIOLA PRODUCING A FEW SHOWERS
OVER THE ISLAND AND SOME DEBRIS HIGH CLOUDINESS ACROSS PUERTO
RICO. OTHERWISE...DRY STABLE AIR DOMINATES.

ATLANTIC OCEAN...
SCATTERED SHOWERS AND TSTMS CONTINUE OVER THE WRN ATLC AND THE
BAHAMAS W OF 76W ASSOCIATED WITH THE MOIST AND UNSTABLE
ENVIRONMENT E OF TROPICAL DEPRESSION TEN IN THE NE GULF AND S OF
THE STATIONARY COASTAL FRONT JUST OFFSHORE THE CAROLINAS AND
GEORGIA. UPPER DIFFLUENCE BETWEEN THE UPPER LOW OVER THE ERN
GULF AND AN UPPER HIGH NEAR 27N72W IS ALSO SUPPORTING THIS
CONVECTIVE ACTIVITY. A WEAK SFC TROUGH...ASSOCIATED WITH THE
REMNANTS OF INGRID...EXTENDS ALONG 29N66W 23N69W. THIS SHALLOW
SYSTEM IS ONLY GENERATING ISOLATED SHOWERS NEAR THE AXIS.

THE MAIN FEATURE IN THE CENTRAL ATLC IS A LONG DRAWN OUT SFC
TROUGH WHICH EXTENDS FROM A NEARLY STATIONARY 1009 MB LOW NEAR
35N47W TO A 1012 MB LOW NEAR 18N56W ALONG 32N46W 25N50W 15N57W.
BASED ON SATELLITE IMAGES AND THE TPW ANIMATION...THE SRN LOW IS
LIKELY PARTIALLY ASSOCIATED WITH THE NRN PORTION OF A TROPICAL
WAVE CURRENTLY IN THE CENTRAL CARIB. THE NRN LOW...NON-TROPICAL
IN NATURE...HAS CHANGED LITTLE SINCE YESTERDAY AND IS BEING
MONITORED FOR SIGNS OF TROPICAL DEVELOPMENT. A SWATH OF MID TO
HIGH LEVEL CLOUDINESS AND ISOLATED SHOWERS ARE WITHIN 240 NM E
OF THE TROUGH AXIS.

THE REMAINDER OF THE E ATLC IS DOMINATED BY TYPICAL SFC RIDGING
S OF A 1027 MB HIGH E OF THE AZORES NEAR 38N21W. THIS IS
PRODUCING LIGHT TO MODERATE NE TRADES E OF 45W...EXCEPT STRONGER
NEAR THE COAST OF NW AFRICA WHERE A TIGHTER PRES GRADIENT
EXISTS. IN FACT...A QSCAT PASS AROUND 20Z DEPICTED 20-25 KT
WINDS NEAR THE COAST FROM 21N-28W. THE NWD MOVING UPPER LOW OVER
THE ERN ATLC NEAR 30N25W HAS GAINED MOISTURE TODAY WITH
SCATTERED SHOWERS POSSIBLE FROM 25N-30N BETWEEN 19W-24W.

WEAK SFC RIDGING WILL GRADUALLY TAKE OVER THE WRN ATLC OVER THE
NEXT COUPLE OF DAYS WHILE STRONGER RIDGING CONTINUES TO SIT
OVER THE E ATLC. CONFLUENCE BETWEEN THE SFC RIDGES WILL ALLOW
BROAD TROUGHING AND SCATTERED SHOWER ACTIVITY TO PERSIST OVER
PARTS OF THE CENTRAL ATLC MAINLY N OF 18N...AND S OF THE
NON-TROPICAL SYSTEM BEING MONITORED WELL E OF BERMUDA.

$$
CANGIALOSI




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