[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 221050
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT SUN 22 AUG 2004

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...WEATHER OBSERVATIONS...RADAR...AND
METEOROLOGICAL ANALYSIS.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1000 UTC.

...TROPICAL WAVES...
TROPICAL WAVE ALONG 19W/20W S OF 20N MOVING W 10 KT. EXTREMELY
WELL DEFINED BROAD AREA OF LOW TO MIDDLE LEVEL ROTATION NOTED IN
MORNING VISIBLE IMAGERY AS WELL AS SURFACE OBSERVATIONS FROM THE
W AFRICAN COAST...THE CAPE VERDE ISLANDS...AND THE FEW SHIPS
REPORTING IN THE REGION. CONVERGENT LOW LEVEL NLY FLOW...W OF
THE WAVE AXIS...IS BUMPING UP AGAINST THE ITCZ HELPING TO
ENHANCE SCATTERED MODERATE CONVECTION FROM 19W TO 27W WITHIN THE
ITCZ. ADDITIONALLY...LOCALIZED CLUSTERS OF MODERATE CONVECTION
ARE STRUGGLING TO DEVELOP NEAR THE MEAN CLOUD SYSTEM CENTER FROM
9N TO 12N BETWEEN 17W AND 23W.

TROPICAL WAVE IS ALONG 36W S OF 20N...ABOUT 680 NM W OF THE CAPE
VERDE ISLANDS...MOVING W 15 KT. WAVE HAS A POORLY DEFINED AXIS
WHICH REMAINS NEARLY INDISCERNIBLE WHEN VIEWED IN THE FIRST
VISIBLE IMAGES THIS MORNING. STRONG SURGE OF SAHARAN DUST...
NOTED IN VISIBLE IMAGES FROM LATE YESTERDAY AND THIS MORNING...
DO APPEAR TO BE TRAILING THIS WAVE PARTICULARLY FROM ABOUT 20N
TO 27N E OF THE WAVE AXIS IN THE ATLC...COINCIDING WELL WITH
RECENT CIMSS SAL TRACKING PRODUCT. LOCATION OF THIS WAVE MAY BE
MASKED DUE TO THE VERY PROMINENT AND MORE WELL DEFINED TROPICAL
WAVE TO THE EAST. CURRENT POSITION IS BASED ON AN INVERTED V
PATTERN IN THE ITCZ AS WELL AS THE LEADING EDGE OF SAHARAN DUST
NOTICEABLE IN VISIBLE IMAGERY THIS MORNING.

CARIBBEAN TROPICAL WAVE ALONG 73W/74W S OF 18N MOVING W 20 KT.
CONVECTIVE ACTIVITY HAS DIMINISHED GREATLY OVER THE LAST SEVERAL
HOURS WITH ONLY LIMITED ACTIVITY REMAINING S OF 13N BETWEEN 71W
AND 75W.

W CARIBBEAN TROPICAL WAVE ALONG 88W S OF 21N MOVING W 20 KT HAS
REACHED THE CENTRAL AMERICAN COAST NEAR BELIZE AND GUATEMALA.
MUCH OF THE CONVECTIVE ACTIVITY ASSOCIATED WITH THIS WAVE HAS
SHIFTED SOUTHWESTWARD INTO THE E PACIFIC BASIN. CLUSTERS OF
WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS PERSISTING S OF 23N
BETWEEN 85W AND 90W OVER PORTIONS OF THE GULF AND NW CARIBBEAN
SEA MAY BE LOOSELY ASSOCIATED WITH THIS WAVE.

...ITCZ...
ITCZ AXIS IS ALONG 8N13W 10N20W 8N25W 12N36W 7N48W 9N61W.
ISOLATED SHOWERS WITHIN 90 NM OF AXIS BETWEEN 37W-53W. SCATTERED
MODERATE CONVECTION WITHIN 90 NM EITHER SIDE OF THE AXIS FROM
19W TO 27W.

...DISCUSSION...
GULF OF MEXICO...
DEEP-LAYERED HIGH PRESSURE IS OVER THE CENTRAL GULF WITH
MOISTURE PLUME EXTENDING ALONG THE PERIPHERY OF THIS RIDGE FROM
SOUTHERN TEXAS NE ALONG THE NORTHERN GULF COAST TO FLORIDA THEN
S DOWN THE PENINSULA BEFORE TURNING SW ACROSS THE LOWER KEYS AND
AND YUCATAN CHANNEL. W OF 88W...MODERATE SUBSIDENCE IS KEEPING
MUCH OF THE GULF QUIET WITH ONLY ISOLATED SHOWERS NOTED. EXPECT
DEVELOPMENT OF LATE AFTERNOON AND EVENING TSTMS ACROSS THE
MOISTURE LADEN PERIPHERY OF THE RIDGE AGAIN TODAY AS THERE HAS
BEEN LITTLE CHANGE IN THE PATTERN OVER THE LAST FEW DAYS.

CARIBBEAN SEA...
UPPER LOW IS BECOMING STRETCHED EAST-NORTHEAST TO WEST-SOUTHWEST
WITH MEAN CENTER NEAR 20N87W AND TROUGHING ELSEWHERE FROM
CENTRAL CUBA TO CENTRAL GUATEMALA. MID/UPPER DRY AIR OVER THE
CENTRAL CARIBBEAN N OF 14N BETWEEN 75W AND 85W IS KEEPING THE
AREA MOSTLY DRY. HOWEVER...UPPER HIGH BUILDING INTO THE E
CARIBBEAN WITH CENTER NEAR BARBADOS IS BEGINNING TO PUSH
MOISTURE FROM INLAND OVER COLOMBIA AND VENEZUELA NORTHWARD INTO
THE EASTERN AND CENTRAL CARIBBEAN SEA. DIVERGENCE ON THE WESTERN
SIDE OF THIS HIGH IN CONJUNCTION WITH MOISTENING MIDDLE TO UPPER
LEVELS SHOULD AID IN REFORMATION OF TSTMS LATER TODAY AS
CARIBBEAN TROPICAL WAVE CONTINUES TO TRACK WESTWARD.

SUBTROPICAL ATLANTIC OCEAN...
NARROW TROUGH IS ALONG 32N74W 23N79W. DIFFLUENT FLOW ALOFT E OF
TROUGH AXIS CONTINUES TO ENHANCE LIMITED SHOWER AND TSTMS
ACTIVITY OVER PORTIONS OF THE CENTRAL BAHAMAS AND WESTERN ATLC
FROM 23N TO 31N BETWEEN 71W AND 78W. MID/UPPER HIGH IS NEAR THE
SE BAHAMAS WITH RELATIVELY BENIGN WEATHER BETWEEN IT AND AN
EASTWARD-MOVING UPPER LOW NEAR 23N60W. FURTHER NE...FAIRLY
VIGOROUS MIDDLE LATITUDE LOW IS NEAR 31N51W AND DRIFTING SLOWLY
SOUTH. GENERALLY WLY FLOW IS BETWEEN 50W-35W WITH PLENTY OF DRY
AIR ACROSS THIS AREA. UPPER RIDGING IS E OF 35W WITH A SMALL
UPPER LOW NEAR THE WESTERN BASE OF THE RIDGE AT 19N36W BEING
FORCED NORTHWARD FROM THE DEEP TROPICS BY THE LARGER SCALE
STEERING OF THE ATLC RIDGE. WEAK SURFACE HIGH BLANKETS MUCH OF
THE REGION WITH A BREAK IN THE RIDGE DUE IN LARGE PART TO THE
REMNANT CIRCULATION ONCE KNOWN AS DANIELLE.

TROPICAL ATLANTIC...
MID/UPPER LOW NEAR 19N36W SERVES AS THE DIVIDING LINE BETWEEN
INCREASING MOISTURE OVER THE TROPICAL E ATLC AND DRY AIR
...SUBSIDENCE...PRESENT W OF 35W. BIT OF WESTERLY SHEAR IS
ENTERING THE WESTERN PARTS OF THE AREA N OF 15N W OF 50W AND IS
DOING SO IN CONJUNCTION WITH SOUTHWARD MOVEMENT OF MIDDLE
LATITUDE LOW CENTER. OTHERWISE SHEAR S OF 15N W OF 35W IS FAIRLY
LIGHT. UPPER HIGH NE OF THE CAPE VERDES CONTINUES TO IMPART WEAK
VERTICAL SHEAR OVER MUCH OF THE E TROPICAL ATLC E OF 28W WHILE
ELSEWHERE BETWEEN 28W AND 35W...SOUTHERLY WINDS E OF THE LOW
NEAR 19N36W ARE CREATING A SLIGHTLY UNFAVORABLE SHEAR
ENVIRONMENT IN THIS AREA.

$$
HOLWEG

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