[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 092359
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SAT SEP 09 2006

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHEASTERN
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...WEATHER OBSERVATIONS...RADAR...
AND METEOROLOGICAL ANALYSIS.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 2315 UTC.

...SPECIAL FEATURE...
THE CENTER OF TROPICAL STORM FLORENCE AT 10/0000 UTC IS NEAR
26.1N 64.6W OR ABOUT 430 MILES...690 KM...SOUTH OF BERMUDA
MOVING NORTHWEST AT 12 KT. THE ESTIMATED MINIMUM CENTRAL
PRESSURE IS 992 MB. THE MAXIMUM SUSTAINED WIND SPEED IS 55 KT
WITH GUSTS TO 65 KT. PLEASE READ THE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC
AND THE PUBLIC ADVISORY UNDER MIATCPAT1/WTNT31 KNHC FOR MORE
DETAILS. FLORENCE IS A LARGE TROPICAL CYCLONE WITH TROPICAL
STORM FORCE WINDS EXTENDING OUTWARD 345 MILES IN THE NE QUADRANT
AND NW QUADRANTS. THE OVERALL SATELLITE APPEARANCE INDICATES
THAT FLORENCE CONTINUES TO BECOME BETTER ORGANIZED WITH
CONVECTION CONSOLIDATING AND BECOMING MORE SYMMETRIC ABOUT THE
CENTER WITH CLOUD TOPS CONTINUING TO COOL TO -85 TO -90 C. NEAR
THE CENTER OF THE CONVECTIVE MASS. OUTFLOW IS VERY IMPRESSIVE
AND IS EXPANDING ESPECIALLY TO THE WEST. HOWEVER REPORTS FROM
THE HURRICANE HUNTER AIRCRAFT EARLIER THIS EVENING INDICATE THAT
LOW-LEVEL CENTER WAS SEVERELY ELONGATED. STRENGTHENING TO A
HURRICANE IS FORECAST AS FLORENCE IS IN A FAVORABLE WARM WATER
AND RELATIVELY LOW SHEAR ENVIRONMENT AS IT TRACKS AROUND THE
PERIPHERY OF THE SUBTROPICAL RIDGE.

...TROPICAL WAVES...

A 1010 MB SFC LOW PRES SYSTEM ASSOCIATED WITH A TROPICAL WAVE IS
ANALYZED NEAR 13N24W. THIS LOW IS MOVING TO THE W NEAR 10 KT.
MUCH OF THE ASSOCIATED CONVECTION LIES TO THE SOUTHWEST OF THE
ANALYZED POSITION FROM 9N-12N BETWEEN 24W-28W.

AN E ATLC TROPICAL WAVE IS ALONG 37W S OF 15N MOVING W 10 TO 15
KT. THIS WAVE IS LOW AMPLITUDE AND HAS LITTLE WAVE STRUCTURE ON
SATELLITE IMAGES. THE NORTHERN EXTENSION OF THIS WAVE IS
EMBEDDED IN SAHARAN DUST. DISORGANIZED SHOWER ACTIVITY HAS
INCREASED SLIGHTLY FROM 7N-11N BETWEEN 32W-43W.

A 1011 MB LOW IS ADDED TO THE 18 UTC ANALYSIS NEAR 9N45W. THIS
CIRCULATION IS EASILY SEEN ON VIS AND SHORTWAVE IMAGES. HOWEVER
THE ASSOCIATED SHOWER ACTIVITY IS MINIMAL AND WELL WEST OF THE
LOW LEVEL CENTER FROM 8N-12N BETWEEN 49W-51W. IN ADDITION...
THIS ACTIVITY IS PROPAGATING AWAY FROM THE CIRCULATION CENTER.

A TROPICAL WAVE IS ALONG 50W FROM 9N-25N MOVING W NEAR 10 KT.
EARLIER THIS WEEK THIS WAVE LOOKED LIKE IT WAS BECOMING ABSORBED
BY THE LARGE CIRCULATION OF FLORENCE. HOWEVER...OVER THE LAST
COUPLE OF DAYS IS HAS DEFINITELY SEPARATED ITSELF. A 1013 MB LOW
IS ALONG THE WAVE NEAR 22N. THE LOW LEVEL CIRCULATION IS
PARTIALLY EXPOSED. SCATTERED MODERATE CONVECTION EXISTS FROM
15N-22N BETWEEN 49W-54W. UPPER LEVEL WINDS COULD BECOME MORE
CONDUCIVE FOR FURTHER DEVELOPMENT.

A TROPICAL WAVE IS IN THE W CARIBBEAN ALONG 88W S OF 21N MOVING
W NEAR 10 TO 15 KT. SLIGHT CYCLONIC TURNING IS SEEN IN THE LOW
LEVEL CLOUDS ABOUT THE WAVE AXIS AND A FAINT INVERTED V-PATTERN
IS SEEN ON INFRARED IMAGES. THIS WAVE ALONG WITH UPPER
DIFFLUENCE AND THE ITCZ IS GENERATING SCATTERED MODERATE
CONVECTION FROM 8N-15N BETWEEN 80W-90W. ANOTHER LINE OF
SCATTERED MODERATE HAS DEVELOPED OVER THE YUCATAN PENINSULA AND
GUATEMALA.

A TROPICAL WAVE ALONG 96W S OF 21N MOVING W 10 KT IS MAINLY IN
THE E PACIFIC REGION. ASSOCIATED CONVECTION IS MAINLY IN THE
ITCZ.

...THE ITCZ...
ITCZ IS CENTERED ALONG 15N17W 11N25W 10N37W 8N47W 11N56W. ALL OF
THE SIGNIFICANT CONVECTION IS DISCUSSED IN THE TROPICAL WAVES
SECTION.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL TROUGH CONTINUES TO MOVE NE AWAY FROM THE AREA AS
MID-UPPER LEVEL RIDGING BUILDS FROM THE WEST WITH AN ANTICYCLONE
CENTERED OVER MEXICO NEAR 22N100W. AT THE SFC...A STATIONARY
FRONT IS LINGERING ACROSS THE N PORTION OF THE REGION EXTENDING
FROM CENTRAL FLORIDA WESTWARD ALONG 28N88W 28N95W. UPPER
DIFFLUENCE AND SFC CONVERGENCE IS GENERATING SCATTERED SHOWERS
AND TSTMS N OF 24N ACROSS THE GULF. THIS MOISTURE ENVELOPE IS
SINKING SLOWLY SOUTHWARD STEERED BY THE DOWNWARD BRANCH OF THE
UPPER ANTICYCLONE. THERE IS SOME DRY AIR ALOFT IN THE BAY OF
CAMPECHE KEEPING SHOWERS RATHER ISOLATED IN THAT AREA. SFC WINDS
ARE FAIRLY LIGHT DUE TO THE WEAK PRES GRAD. SHOWERS AND TSTMS
APPEAR LIKELY TO CONTINUE IN THE N GULF TOMORROW NEAR THE SFC
BOUNDARY. GFS DEVELOPS A WEAK LOW ALONG THE FRONT BUT MANY OF
THE OTHER MODELS DO NOT SHOW THIS FEATURE. THIS FRONT WILL BEGIN
TO SLOWLY DISSIPATE OVER THE NEXT COUPLE OF DAYS.

CARIBBEAN SEA...
THE SOUTHERN PORTION OF A LARGE ATLC SUBTROPICAL RIDGE COVERS
THE NE CARIBBEAN. A WEAK UPPER HIGH IS CENTERED OVER EASTERN
CUBA AND AN ILL-DEFINED WEAKENING UPPER LEVEL LOW IS LOCATED
ABOUT 300 NM TO THE N OF HISPANIOLA. THE DEEPEST TROPICAL
MOISTURE IS IN THE SW CARIBBEAN WHERE NUMEROUS SHOWERS AND TSTMS
ARE FOUND S OF 14N BETWEEN 78W-86W. THIS MOISTURE IS HIGHLY
CONTRIBUTED TO THE ITCZ WITH PERHAPS SOME ENHANCEMENT FROM A
TROPICAL WAVE TO THE WEST. SHOWERS AND TSTMS HAVE ALSO FIRED UP
THIS AFTERNOON OVER JAMAICA AND CUBA ASSOCIATED WITH SOME UPPER
DIFFLUENCE AND LOCAL SMALL SCALE EFFECTS. A LINE OF SHOWERS AND
TSTMS HAS ALSO DEVELOPED OVER THE YUCATAN PENINSULA AND
GUATEMALA FROM 16N-20N BETWEEN 88W-89W.  A FAIR AMOUNT OF HIGH
LEVEL MOISTURE COVERS THE AREA W OF 75W WITH MUCH DRIER AIR
NOTED ON WATER VAPOR IMAGES E OF THERE. SFC WINDS ARE
SOUTHWESTERLY ACROSS THE LESSER ANTILLES...DUE TO THE VERY LARGE
CIRCULATION OF FLORENCE...WHICH IS LOCATED SEVERAL HUNDRED MILES
N OF THE AREA. FAIRLY LIGHT TYPICAL EASTERLIES EXIST IN THE
CENTRAL AND WESTERN CARIBBEAN.

ATLANTIC OCEAN...
AN UPPER LEVEL TROUGH IS TRACKING EASTWARD ALONG AND JUST OFF
THE E COAST OF THE U.S. AN ASSOCIATED COLD FRONT ENTERS THE AREA
NEAR 32N72W AND EXTENDS TO NEAR MELBOURNE FLORIDA. ONLY ISOLATED
SHOWERS ARE NEAR THE FRONT IN THE ATLC LIKELY BECAUSE OF THE DRY
AIR ALOFT ABOVE THE AREA. MUCH MORE ACTIVITY EXISTS NEAR THE
FRONT IN THE GULF. A LARGE SUBTROPICAL RIDGE COVERS THE REGION
BETWEEN 40W-70W. THE UPPER TROUGH ALONG THE E COAST U.S. IS
WEAKENING THE WESTERN EXTENSION OF THE RIDGE. THESE ARE THE MAIN
STEERING COMPONENT FOR TROPICAL STORM FLORENCE WHICH LIES ON THE
W PERIPHERY OF THE RIDGE. A VERY WEAK UPPER LEVEL LOW IS LOCATED
JUST AHEAD OF FLORENCE NEAR 26N73W. A SHARP UPPER LEVEL TROUGH
LIES TO THE E OF THE RIDGE AND COVERS THE REGION BETWEEN 25W-40W
WITH AN UPPER LOW CENTER NEAR 26N33W. THIS UPPER LEVEL FEATURE
HAS A SFC REFLECTION AS A TROF ALONG 26N32W 32N29W. THIS TROUGH
LOOKS LIKE IT IS BECOMING CUT OFF AS A RATHER LARGE RIDGE BUILDS
OFF THE COAST OF AFRICA WITH THE AXIS ALONG 25N. A LARGE AREA OF
SCATTERED MODERATE CONVECTION ASSOCIATED WITH FLORENCE LIES FROM
23N-29N BETWEEN 60W-69W.  ACCORDING TO THE CIMSS SAL TRACKING
PRODUCT AND THE MILKY LOOK ON THE EARLIER VIS IMAGES THE SAHARAN
DUST HAS SPREAD TO NEAR 50W...HOWEVER THIS DUST APPEARS TO BE
CONSIDERABLY MORE DIFFUSE THAN EARLIER THIS SEASON. A 1024 MB
SFC HIGH PRES SYSTEM IS LOCATED NEAR 35N47W. THE TIGHTEST PRES
GRAD IS IN THE CENTRAL ATLC NEAR T.S. FLORENCE WHICH IS
PRODUCING A LARGE AREA OF TROPICAL STORM FORCE WINDS TO THE N OF
THE CYCLONE.

$$
CANGIALOSI




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