[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 031758
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU SEP 03 2009

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...

TROPICAL STORM ERIKA IS CENTERED NEAR 16.6N 64.7W AT 03/1800 UTC
OR ABOUT 70 NM S OF ST. CROIX AND ABOUT 135 NM SE OF SAN JUAN
PUERTO RICO MOVING W AT 8 KT. ESTIMATED MINIMUM CENTRAL PRESSURE
IS 1008 MB. MAXIMUM SUSTAINED WIND SPEED IS 35 KT WITH GUSTS TO
45 KT. NUMEROUS MODERATE/SCATTERED STRONG CONVECTION IS FROM
13N-19N BETWEEN 60W-64W. SEE LATEST NHC INTERMEDIATE PUBLIC
ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT1/WTNT31 KNHC AND THE
FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21
KNHC FOR MORE DETAILS.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 17W S OF 16N MOVING W NEAR 15 KT. A 1012
MB LOW IS ALONG THE WAVE AXIS NEAR 11N AND HAS BEEN TRACKING TO
THE WNW OVER THE PAST 24 HOURS. UPPER AIR TIME SECTION ANALYSES
FROM BAMAKO MALI DEPICTED THAT THIS WAVE PASSED AROUND 02/1200
UTC WITH A STRONG ANOMALOUS WIND SHIFT SIGNATURE FROM THE
SURFACE TO 500 MB...INDICATIONS OF A VIGOROUS AND DEEP LAYERED
TROPICAL WAVE. VISIBLE SATELLITE AND CIMSS WAVETRAK MODEL
GUIDANCE SHOW BROAD CYCLONIC TURNING ALONG THE WAVE AXIS BETWEEN
12W-24W. SCATTERED MODERATE CONVECTION IS FROM 6N-12N BETWEEN
13W-24W WITH SCATTERED SHOWERS COVERING A LARGER AREA FROM
6N-17N BETWEEN 12W-25W.

TROPICAL WAVE IS ALONG 32W S OF 19N MOVING W NEAR 15 KT. A 1014
MB LOW IS ALONG THE WAVE AXIS NEAR 14N. THE WAVE COINCIDES WITH
A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE
WATER IMAGERY...HOWEVER...VISIBLE SATELLITE IMAGERY INDICATES A
DRY SAHARAN AIR LAYER SURROUNDING THE WAVE...THUS INHIBITING ANY
SIGNIFICANT DEEP CONVECTION. MOST SCATTERED SHOWERS AND WIDELY
SCATTERED MODERATE CONVECTION ARE EMBEDDED WITHIN THE ITCZ FROM
5N-11N BETWEEN 26W-36W.

TROPICAL WAVE IS ALONG 47W S OF 15N MOVING W 10-15 KT. THE WAVE
REMAINS LOW-AMPLITUDE AND EMBEDDED WITHIN THE ITCZ AT THE
LEADING EDGE OF A MOISTURE MAXIMUM AS INDICATED BY THE TPW
IMAGERY. CONVECTION IS LIMITED TO ISOLATED SHOWERS FROM 11N-14N
BETWEEN 45W-49W.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 10N18W 10N30W 9N33W 9N44W 8N48W
8N60W. ASIDE FROM THE CONVECTION ASSOCIATED WITH THE TROPICAL
WAVES IN THE TROPICAL ERN ATLC...SCATTERED MODERATE CONVECTION
IS WITHIN 90 NM ON EITHER SIDE OF THE AXIS BETWEEN 38W-44W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER LEVEL TROUGH COVERS THE ERN CONUS AND DIPS SWD INTO THE
GULF WITH AN AXIS ALONG 87W TO THE YUCATAN CHANNEL. THIS UPPER
TROUGH SUPPORTS A 1012 MB SURFACE LOW CENTERED IN THE NE GULF
NEAR 27N86W. A SURFACE TROUGH EXTENDS ACROSS THE CENTRAL FLORIDA
PENINSULA INTO THIS SURFACE LOW AND CONTINUES SW FROM THE LOW
ALONG 24N87W TO 22N92W. LOW-LEVEL CONVERGENCE NEAR THE SURFACE
LOW AND MIDDLE TO UPPER LEVEL LIFT ASSOCIATED WITH THE UPPER
LEVEL TROUGH ARE GENERATING SCATTERED SHOWERS AND ISOLATED TSTMS
ACROSS THE NE GULF N OF 25N E OF 88W AND ALSO WITHIN 120 NM OF
THE SURFACE TROUGH ACROSS THE SRN GULF. AN UPPER RIDGE IS
ANCHORED IN THE E PACIFIC AND EXTENDS ACROSS CENTRAL MEXICO AND
THE ERN BAY OF CAMPECHE. SCATTERED SHOWERS AND ISOLATED TSTMS
ARE ACROSS THE SW GULF AND BAY OF CAMPECHE SW OF A LINE FROM
24N98W TO 20N92W. A WEAK SURFACE RIDGE IS ALONG THE NW GULF
COAST AND CONTINUES TO BE SUPPORTED BY NWLY FLOW AND A DRY...
SUBSIDENT AIRMASS ALOFT ON THE WRN EXTENT OF THE UPPER TROUGH
ALONG 88W. GENERALLY FAIR WEATHER IS ASSOCIATED WITH THIS
FEATURE ACROSS THE NW GULF.

CARIBBEAN SEA...
A MAIN CONCERN IS TROPICAL STORM ERIKA OVER THE LESSER ANTILLES
AND NE CARIBBEAN. THE CONVECTION ASSOCIATED WITH ERIKA IS
SUPPORTED ALOFT BY UPPER LEVEL DIVERGENCE PROVIDED BY AN UPPER
LEVEL ANTICYCLONIC CIRCULATION CENTERED NEAR 14N65W. THE UPPER
LEVEL RIDGE COVERS MUCH OF THE ERN CARIBBEAN E OF 72W. FARTHER
TO THE W...THE UPPER LEVEL TROUGH IMPACTING THE GULF OF MEXICO
EXTENDS THROUGH THE YUCATAN CHANNEL TO 14N80W WITH A WEAK UPPER
LEVEL LOW E OF THE MAIN TROUGH AXIS CENTERED NEAR 20N74W. MOSTLY
DRY AIR ALOFT AND THE REMAINS OF A SAHARAN AIR LAYER MOVING
ACROSS THE WRN CARIBBEAN IS KEEPING RELATIVELY CLEAR SKIES N OF
12N W OF 72W. HOWEVER...A FEW SCATTERED SHOWERS AND ISOLATED
TSTMS ARE NOTED ON SATELLITE IMAGERY IN THE SW CARIBBEAN S OF
12N AND ACROSS PANAMA...AS WELL AS A FEW ISOLATED SHOWERS OVER
THE NW CARIBBEAN AS THE SURFACE TROUGH ACROSS THE S/CENTRAL GULF
OF MEXICO CONTINUES DRIFTING SEWD.

ATLANTIC OCEAN...
A 1013 MB LOW IS CENTERED IN THE W ATLC NEAR 32N76W WITH A
SURFACE TROUGH EXTENDING SW TO VERO BEACH FLORIDA AND INTO THE
NE GULF OF MEXICO. SCATTERED SHOWERS ARE WITHIN 90 NM EITHER
SIDE OF THE SURFACE TROUGH. ANOTHER SURFACE TROUGH EXTENDS FROM
25N77W TO 31N75W. SCATTERED SHOWERS AND TSTMS ARE FROM 22N-32N
BETWEEN 72W-79W. STRONG MIDDLE TO UPPER LEVEL MOIST SLY FLOW
ALOFT AND UPPER DIFFLUENCE IS FURTHER ENHANCING THE CONVECTION
ACROSS THE W ATLC. TO THE EAST OF THIS ACTIVITY...A BROAD UPPER
LEVEL RIDGE COVERS THE REMAINDER OF THE W ATLC ANCHORED NEAR
31N69W. A UPPER LEVEL LOW IS CENTERED NEAR 26N60W. UPPER LEVEL
DIFFLUENCE E OF THE UPPER LOW IS GENERATING SCATTERED SHOWERS
FROM 24N-29N BETWEEN 50W-56W. THE REMAINDER OF THE CENTRAL AND
ERN ATLC IS DOMINATED BY RATHER BENIGN UPPER LEVEL FEATURES AND
A BROAD SURFACE RIDGE N OF 22N W OF 70W. THIS SURFACE RIDGE IS
ANCHORED BY A 1026 MB HIGH N OF THE REGION CENTERED NEAR 33N42W.

$$
HUFFMAN




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