[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 271331 RRA
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT THU JUL 27 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1300 UTC.

...TROPICAL WAVES...

A TROPICAL WAVE IS ADDED TO THE 06 UTC SURFACE ANALYSIS ALONG
19W SOUTH OF 18N MOVING WEST NEAR 15 KT. THIS WAVE WAS ADDED
BASED UPON THE LOW LEVEL CYCLONIC WIND SHIFT IN THE DAKAR
SOUNDINGS BETWEEN 11 UTC AND 23 UTC YESTERDAY AND THE IMPRESSIVE
LOW-MID LEVEL TURNING EVIDENT ON THE FIRST FEW VISIBLE PICTURES
THIS MORNING.  IN ADDITION...GFS HAS A GOOD HANDLE ON THIS WAVE
ALREADY AND SUGGESTS THAT IT MAY BECOME HIGH AMPLITUDE IN THE
NEXT DAY OR TWO. SCATTERED MODERATE CONVECTION IS EMBEDDED
WITHIN THE ITCZ FROM 6N-13N BETWEEN 11W-31W.

BASED UPON SATELLITE IMAGERY AND THE AVAILABLE DATA...THE
TROPICAL WAVE IN THE EASTERN ATLANTIC PREVIOUSLY ALONG 31W AT 18
UTC YESTERDAY HAS BEEN DROPPED FROM THE SURFACE ANALYSIS. THIS
FEATURE DOES NOT APPEAR TO HAVE BEEN A TROPICAL WAVE BUT RATHER
SOME INSTABILITY LEFT BEHIND FROM THE BROAD HIGH AMPLITUDE WAVE
600-700 NM TO ITS WEST.

A HIGH AMPLITUDE TROPICAL WAVE IS ALONG 46W SOUTH OF 21N MOVING
WEST NEAR 20 KT. THIS LARGE WAVE REMAINS WELL DEFINED WITH CLEAR
LOW-MID LEVEL TURNING EVIDENT ON SATELLITE IMAGERY. THE WAVE IS
ENHANCING CONVECTION EMBEDDED WITHIN THE ITCZ FROM 5N-12N
BETWEEN 35W-53W. THE NORTHERN EXTENSION OF THE WAVE HAS LIMITED
SHOWER ACTIVITY AS IT IS EMBEDDED IN A DRY/STABLE ENVIRONMENT
LIKELY DUE TO SAHARAN DUST.

A HIGH AMPLITUDE TROPICAL WAVE IS IN THE EASTERN CARIBBEAN ALONG
66W SOUTH OF 23N MOVING WEST 15-20 KT. THIS WAVE HAS BEEN
WELL-DEFINED OVER THE PAST SEVERAL DAYS. SHOWER AND TSTM
ACTIVITY HAS INCREASED TODAY WITH PATCHES OF SCATTERED MODERATE
CONVECTION MAINLY BEHIND THE WAVE AXIS ACROSS PUERTO RICO...THE
VIRGIN ISLANDS...LEEWARD AND WINDWARD ISLANDS FROM 13-23N
BETWEEN 60W-69W. AN INCREASE IN WINDS IS EVIDENT BEHIND THE WAVE
AXIS BASED ON AN EARLIER QUIKSCAT PASS AND BUOY/SHIP OBS.
FURTHER DEVELOPMENT IS NOT LIKELY TO OCCUR AS UPPER LEVEL WINDS
ARE HIGHLY UNFAVORABLE.

A WESTERN CARIBBEAN SEA TROPICAL WAVE IS ALONG 83W/84W SOUTH OF
18N MOVING WEST NEAR 15 KT. VERY LITTLE WAVE SIGNATURE IS NOTED
ON SATELLITE IMAGERY. HOWEVER...THIS WAVE MAY BE AIDING IN
TRIGGERING CLUSTERS OF MODERATE/STRONG CONVECTION EMBEDDED IN
THE ITCZ ACROSS THE SOUTHERN CARIBBEAN FROM 5N-12N BETWEEN
73W-83W.

...ITCZ...
ITCZ AXIS IS CENTERED ALONG 11N15W 10N30W 11N45W TO INLAND OVER
SOUTH AMERICA NEAR 10N63W TO PANAMA NEAR 9N82W. ALL OF THE
SIGNIFICANT AREAS OF CONVECTION IS ASSOCIATED WITH OR ENHANCED
BY TROPICAL WAVES AND IS DISCUSSED IN THE ABOVE SECTION.

...DISCUSSION...
GULF OF MEXICO...
THE SURFACE LOW THAT HAS BEEN MOVING NORTHWARD ALONG THE
MEXICO/TEXAS COAST OVER THE PAST FEW DAYS HAS DISSIPATED. DURING
THE OVERNIGHT HOURS...THERE WERE PATCHES OF MODERATE CONVECTION
ACROSS PORTIONS OF NRN MEXICO...SOUTH TEXAS...WRN LOUISIANA AND
THE COASTAL WATERS. SINCE THEN...MUCH OF THE ACTIVITY HAS
WEAKENED CONSIDERABLY LEAVING ONLY SCATTERED SHOWERS AND TSTMS
IN THE NW GULF W OF 93W N OF 23N. THESE LEFT OVER SHOWERS ARE
CAUSED BY WEAK LOW LEVEL CONVERGENCE AND UPPER DIFFLUENCE
BETWEEN AN UPPER HIGH IN THE CENTRAL GULF AND AN UPPER LOW OVER
NRN MEXICO. THE UPPER HIGH IS ADVECTING SOME OF THE MOISTURE
FROM THE W GULF ACROSS THE SE U.S. AND NRN GULF...HOWEVER MUCH
OF IT IS MAINLY IN THE UPPER LEVELS. MOISTURE IS SLIGHTLY DEEPER
WITH EMBEDDED SCATTERED SHOWERS/TSTMS ACROSS FLORIDA AND THE SE
GULF AS THERE IS SOME UPPER DIFFLUENCE BETWEEN THE GULF OF
MEXICO HIGH AND A TROUGH OFF THE SE U.S. AT THE
SURFACE...RIDGING HAS BUILT ACROSS THE REGION FROM THE
BERMUDA-AZORES HIGH TO A 1018 MB HIGH OVER THE FL/GA BORDER. SFC
FLOW IS LIGHT ACROSS FLORIDA AND THE E GULF...STRONGER W OF 87W
WHERE SE WINDS OF 15-20 KT ARE COMMON. THE REMNANT MOISTURE IN
THE W GULF WILL CONTINUE TO DRIFT NWD AND BECOME ISOLATED.
COMPUTER MODELS INCREASE MOISTURE SLIGHTLY OVER FLORIDA AND THE
E GULF LATER TODAY ASSOCIATED WITH THE DIGGING UPPER TROUGH OFF
THE U.S. EAST COAST. LITTLE CHANGE IN THE SURFACE PATTERN IS
EXPECTED OVER THE NEXT FEW DAYS AS SFC RIDGING IS LIKELY TO
REMAIN ESTABLISHED.

CARIBBEAN SEA...
TWO TROPICAL WAVES ARE IN THE CARIBBEAN SEA THIS MORNING. THE
WESTERN-MOST WAVE IS ALONG 83W/84W ENHANCING CONVECTIVE ACTIVITY
IN THE ITCZ ACROSS THE SOUTHERN CARIBBEAN. SEE THE TROPICAL
WAVES SECTION FOR MORE DETAILS. THE OTHER WAVE...ALONG 66W...IS
MORE IMPRESSIVE INTERACTING WITH AN UPPER LEVEL LOW IN THE ATLC
TO PRODUCE A RATHER WIDE AREA OF SHOWERS AND TSTMS ACROSS THE
LESSER ANTILLES AND PUERTO RICO FROM 13N-23N BETWEEN 60W-69W.
PUERTO RICO DOPPLER RADAR SHOWS BANDS OF SHOWERS AND TSTMS
MOVING WWD TO THE N OF THE ISLAND WITH A MUCH LARGER SHIELD OF
MODERATE TO HEAVY RAIN OVER THE EASTERN PORTION OF PUERTO RICO
AND THE VIRGIN ISLANDS. THIS WAVE WILL CONTINUE TO MOVE QUICKLY
TO THE WEST...STEERED BY THE STRONG SFC HIGH...SPREADING
MOISTURE ACROSS THE CENTRAL CARIBBEAN LATER TODAY AND WESTERN
CARIBBEAN ON FRI. AN UPPER LOW IS MOVING TO THE WSW IN THE WRN
CARIBBEAN CENTERED NEAR 18N86W. WEAK UPPER DIFFLUENCE BETWEEN
THIS UPPER LOW AND THE GULF OF MEXICO UPPER HIGH IS TRIGGERING
SCATTERED SHOWERS/ISOLATED TSTMS OVER SOUTH CUBA AND THE CAYMAN
ISLANDS FROM 19N-21N BETWEEN 76W-86W. TRADE WINDS ARE GENERALLY
IN THE 15-20 KT RANGE WITH SOME SLIGHTER STRONGER WINDS OFF THE
COAST OF COLOMBIA AND POSSIBLY IN THE CONVECTION ACROSS THE
LESSER ANTILLES.

ATLANTIC OCEAN...
A BERMUDA-AZORES SURFACE RIDGE RUNS FROM A 1027 MB HIGH
PRESSURE CENTER OVER THE AZORES TO A 1030 MB HIGH IN THE CENTRAL
ATLC NEAR 34N54W ACROSS BERMUDA INTO THE CENTRAL GULF OF MEXICO.
A WEAK BENIGN 1021 MB SURFACE LOW PRESSURE CENTER IS
CONTAMINATING THE RIDGE NEAR 30N31W AS IT DRIFTS SWD. IN THE
UPPER LEVELS...A TROUGH OFF THE SE U.S. INTERACTING WITH AN
UPPER HIGH IN THE GULF IS PRODUCING A CONSIDERABLE AMOUNT OF
UPPER LEVEL MOISTURE W OF 72W N OF 24N. ONLY SCATTERED SHOWERS
AND ISOLATED TSTMS ARE EMBEDDED IN THIS MOISTURE PLUME. A
WELL-DEFINED UPPER LOW IS CENTERED NEAR 27N65W. THIS UPPER LOW
IS INTERACTING WITH THE EASTERN CARIBBEAN TROPICAL WAVE TO
PRODUCE A LARGE AREA OF SCATTERED MODERATE CONVECTION. SEE THE
CARIBBEAN SECTION FOR MORE DETAILS. A VERY WEAK DRY UPPER LOW IS
MOVING NWD OUT OF THE DISCUSSION AREA NEAR 33N56W. A BROAD UPPER
RIDGE COVERS A LARGE PORTION OF THE ATLC N OF 10N BETWEEN 18W
AND 55W. MIDDLE TO UPPER LEVEL DRY/STABLE AIR IS NORTH OF 14N
BETWEEN 25W AND 55W. AN UPPER TROUGH CLIPS THE AREA E OF 18W N
OF 27N. A WIDESPREAD AREA OF DENSE SAHARAN DUST EXTENDS OUT TO
ABOUT 65W...BEHIND THE E CARIBBEAN TROPICAL WAVE. THE
COMBINATION OF THE DRY/STABLE ATMOSPHERE FROM THE SAHARAN DUST
AND SUBSIDENCE FROM UPPER RIDGING IS SUPPRESSING ANY SIGNIFICANT
CONVECTION IN THE ATLC N OF THE ITCZ.

$$
CANGIALOSI


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