[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 220553
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0530 UTC.

...TROPICAL WAVES...
TROPICAL WAVE ALONG 18W/19W S OF 20N MOVING W 10 KT. EXTREMELY
WELL DEFINED BROAD AREA OF LOW TO MIDDLE LEVEL ROTATION NOTED IN
INFRARED IMAGERY AS WELL AS SURFACE OBSERVATIONS FROM THE W
AFRICAN COAST...THE CAPE VERDE ISLANDS...AND LIMITED SHIPS IN
THE AREA. CONVERGENT LOW LEVEL FLOW W OF THE WAVE AXIS IS
HELPING TO ENHANCE SCATTERED MODERATE CONVECTION FROM 18W TO 27W
WITHIN THE ITCZ TONIGHT. ADDITIONALLY...SOME VERY LOCALIZED
CLUSTERS OF MODERATE CONVECTION ARE STRUGGLING TO DEVELOP NEAR
THE MEAN CLOUD SYSTEM CENTER AND OVER THE RELATIVELY COOLER
WATERS OF THE E TROPICAL ATLC.

TROPICAL WAVE IS ALONG 34W S OF 20N...ABOUT 600 NM W OF THE CAPE
VERDE ISLANDS...MOVING W 15 KT. WAVE HAS A POORLY DEFINED AXIS
IN SATELLITE IMAGERY AND MAY BE MASKED A BIT DUE TO THE VERY
PROMINENT AND MORE WELL DEFINED TROPICAL WAVE TO THE EAST.
CURRENT POSITION BASED ON AN INVERTED V PATTERN IN THE ITCZ AS
WELL AS SOME VERY LIMITED MID-LEVEL TURNING NOTED IN THE IR
IMAGERY. A VERY STRONG SURGE OF SAHARAN DUST...NOTED IN VISIBLE
IMAGES FROM LATE YESTERDAY...DOES APPEAR TO BE TRAILING THIS
WAVE PARTICULARLY FROM ABOUT 20N TO 27N E OF THE WAVE AXIS IN
THE ATLC. THIS COINCIDES WELL WITH CIMSS SAL TRACKING PRODUCT
FROM TONIGHT.

CARIBBEAN TROPICAL WAVE ALONG 72W S OF 18N MOVING W 20 KT.
YESTERDAYS CONVECTIVE ACTIVITY PRIMARILY E OF THE WAVE
AXIS...APPEARS TO HAVE SHIFTED TO POSITION MORE ALONG AND EVEN W
OF THE WAVE AXIS WITH NUMEROUS STRONG CONVECTION FOUND S OF 13N
E OF 77W OFFSHORE AND INLAND OVER PORTIONS OF NORTHERN COLOMBIA.
FURTHER E OF THE WAVE AXIS...INFRARED IMAGERY CONTINUES TO
INDICATE A FAIRLY LARGE AREA OF OVERCAST LOW TO MIDDLE LEVEL
CLOUDS WITH WIDELY SCATTERED EMBEDDED SHOWERS AND TSTMS S OF 15N
BETWEEN 72W AND 68W.

W CARIBBEAN TROPICAL WAVE ALONG 86W S OF 21N MOVING W 20 KT.
MUCH OF THE CONVECTIVE ACTIVITY ASSOCIATED WITH THIS WAVE HAS
SHIFTED WESTWARD INTO THE E PACIFIC BASIN. CLUSTERS OF WIDELY
SCATTERED SHOWERS AND ISOLATED TSTMS DO PERSIST S OF 23N AND W
OF 85W OVER PORTIONS OF THE GULF AND NW CARIBBEAN SEA TONIGHT.

...ITCZ...
ITCZ AXIS IS ALONG 9N13W 9N21W 12N34W 8N43W 10N62W. ISOLATED
SHOWERS WITHIN 60 NM OF AXIS BETWEEN 37W-50W. SCATTERED MODERATE
CONVECTION WITHIN 90 NM EITHER SIDE OF THE AXIS FROM 18W TO 27W.
DISSIPATING SCATTERED MODERATE WITHIN 60 NM EITHER SIDE OF THE
AXIS FROM 36W TO 43W.

...DISCUSSION...
GULF OF MEXICO...
DEEP-LAYERED HIGH PRESSURE IS OVER THE CENTRAL GULF WITH TSTMS
FORMING ON THE N AND E SIDE OF THE RIDGING OVER THE DEEP SOUTH
INTO FLORIDA AND EXTENDING SW ACROSS THE LOWER KEYS TOWARD THE
YUCATAN CHANNEL. W OF 88W...MODERATE SUBSIDENCE IS KEEPING THE
REMAINDER OF GULF WATERS RATHER QUIET WITH ONLY ISOLATED SHOWERS
NOTED. EXPECT SIMILAR CONDITIONS ACROSS MUCH OF THIS AREA INTO
MON AS LITTLE CHANGE IN THE PATTERN IS EXPECTED.

CARIBBEAN SEA...
UPPER LOW IS NEAR 20N86W WITH TROUGHING FROM CENTRAL CUBA TO N
BELIZE. LIMITED INSTABILITY ASSOCIATED WITH THE TROUGH IS
ALLOWING FOR WIDELY SCATTERED SHOWERS AND ISOLATED TSTMS N OF
18N W OF 80W. MID/UPPER DRY AIR OVER THE CENTRAL CARIBBEAN N OF
13N BETWEEN 73W AND 83W IS KEEPING THE AREA MOSTLY DRY. UPPER
HIGH IS BUILDING INTO THE E CARIBBEAN WITH CENTER NEAR BARBADOS.
DIVERGENCE ON THE WESTERN SIDE OF THE HIGH SHOULD ALLOW
REFORMATION OF TSTMS LATER TODAY AS PREVIOUS WESTERLY SHEAR OVER
THE TROPICAL WAVE IN THE AREA HAS SHIFTED TO BECOME MORE OF A
SOUTHERLY COMPONENT...AND LESS DETRIMENTAL TO TSTM DEVELOPMENT.

SUBTROPICAL ATLANTIC OCEAN...
NARROW TROUGH IS ALONG 32N75W TO 23N80W. DIFFLUENT FLOW ALOFT E
OF TROUGH AXIS CONTINUES TO ENHANCE LIMITED SHOWER AND TSTMS
ACTIVITY OVER PORTIONS OF THE SOUTHERN AND CENTRAL BAHAMAS.
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 32N52W
AND DRIFTING SLOWLY SOUTH. GENERALLY WLY FLOW IS BETWEEN 50W-35W
WITH PLENTY OF DRY AIR. UPPER RIDGING IS E OF 35W WITH A SMALL
UPPER LOW NEAR THE WESTERN BASE OF THE RIDGE AT 18N35W 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 TO THE REMNANT
CIRCULATION ONCE KNOWN AS DANIELLE.

TROPICAL ATLANTIC...
MID/UPPER LOW NEAR 18N35W IS THE DIVIDING LINE BETWEEN
INCREASING MOISTURE OVER THE TROPICAL E ATLC AND DRY AIR
...SUBSIDENCE...PRESENT W OF 35W.  A BIT OF WESTERLY SHEAR IS
COMING INTO THE WESTERN PART OF THE AREA N OF 15N W OF 50W IN
CONJUNCTION WITH SOUTHWARD MOVEMENT OF MIDDLE LATITUDE LOW
CENTER...OTHERWISE SHEAR W 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.
ELSEWHERE IN THIS AREA BETWEEN 28W AND 35W...SOUTHERLY WINDS E
OF THE LOW NEAR 18N35W ARE CREATING A SLIGHTLY UNFAVORABLE SHEAR
ENVIRONMENT IN THIS AREA.

$$
HOLWEG

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