[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 110544
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT SAT AUG 11 2007

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

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0515 UTC.

...TROPICAL WAVES...

HIGH AMPLITUDE TROPICAL WAVE IS JUST MOVING OUT OF THE AFRICAN
COAST. IT AXIS IS ALONG 15W S OF 22N WITH A 1008 MB LOW PRES
NEAR 13N. STRONG CLUSTERS OF MODERATE TO ISOLATED STRONG
CONVECTION ARE AHEAD OF THE WAVE AXIS COVERING FROM 10N-14N E OF
19W. SOME OF THE COMPUTER MODELS DEVELOP THIS LOW INTO A
TROPICAL CYCLONE AS IT MOVES WWD ACROSS THE ATLANTIC OCEAN.

TROPICAL WAVE IS ALONG 28W S OF 17N MOVING W 5-10 KT. THIS WEAK
FEATURE HAS BEEN EMBEDDED IN VERY LIGHT STEERING OVER THE PAST
24 HOURS. IT IS EXPECTED TO SPEED UP SHORTLY AS AN ELY JET SETS
UP IN THIS REGION. CURRENT SATELLITE IMAGES SHOW LITTLE WAVE
SIGNATURE...SO THE CURRENT POSITION IS BASED ON SLOW FORWARD
EXTRAPOLATION WHICH AGREES WELL WITH A NEARLY STATIONARY
MOISTURE BUMP SEEN IN THE SSMI-DERIVED TOTAL PRECIPITABLE WATER.

TROPICAL WAVE IS ALONG 44W S OF 14N MOVING W 10-15 KT. THIS LOW
AMPLITUDE WAVE REMAINS WEAK CAUSING A VERY SLIGHT PERTURBATION
IN THE ITCZ. SCATTERED SHOWERS ARE ASSOCIATED WITH THIS FEATURE.

HIGH AMPLITUDE TROPICAL WAVE IS ALONG 67/68W S OF 21N MOVING W
NEAR 15 KT. THIS WAVE WAS PREVIOUSLY ALONG 65W ON THE 00Z SFC
MAP...BUT EARLIER QUIKSCAT PASS AND LATEST SFC DATA SHOW THAT
THE WAVE AXIS IS FURTHER WEST ALONG THE MONA PASSAGE. THIS
FEATURE IS GENERATING AN AREA OF SHOWERS WITH EMBEDDED TSTMS
OVER DOMINICAN REPUBLIC AND THE REGIONAL COASTAL WATERS. THIS
WAVE IS ALSO INTERACTING WITH AN UPPER LOW OVER THE BAHAMAS. THE
SAN JUAN DOPPLER RADAR DEPICTS SCATTERED SHOWERS AND ISOLATED
TSTMS BEHIND THE WAVE AXIS AFFECTING PUERTO RICO AND THE COASTAL
WATERS. AS THE DAY GOES ON...MOISTURE FROM THIS WAVE SHOULD
SPREAD FIRST OVER THE REMAINDER OF HISPANIOLA AND AFTERWARD
OVER THE BAHAMAS AND EASTERN CUBA.

TROPICAL WAVE IS ALONG 75W/76W S OF 19N MOVING W NEAR 15 KT.
THIS WAVE IS PROBABLY ENHANCING SOME SHOWER ACTIVITY OVER
EASTERN CUBA AND JAMAICA. THE SSMI-DERIVED TOTAL PRECIPITABLE
WATER SHOW AN ENHANCED WWD MOVING MOISTURE SURGE IN AN
ALREADY HIGH TPW ENVIRONMENT. THIS IS MAIN SOURCE USED TO TRACK
THIS FEATURE.

TROPICAL WAVE IS OVER THE YUCATAN PENINSULA AND GUATEMALA ALONG
90W/91W S OF 20N MOVING W 10-15 KT. THIS WAVE LIES UNDERNEATH AN
UPPER LOW WHICH IS HELPING TO GENERATE SCATTERED SHOWERS AND
ISOLATED TSTMS WITHIN 90 NM OF THE AXIS...PARTICULARLY OVER EL
SALVADOR.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 10N17W 11N26W 11N36W 11N60W.
CLUSTERS OF MODERATE TO ISOLATED STRONG CONVECTION ARE JUST OFF
THE AFRICAN COAST FROM 10N-14N E OF 19W...ASSOCIATED WITH A
LARGE TROPICAL WAVE MAKING ITS WAY TO THE COAST. SCATTERED
MODERATE CONVECTION IS NEAR 8N22W AND WITHIN 60 NM EITHER SIDE W
OF 40W.

DISCUSSION...
GULF OF MEXICO...
THE COMBINATION OF A STRONG UPPER HIGH OVER THE SRN U.S. AND AN
UPPER LOW OVER THE SW CORNER OF THE GULF NEAR 21N94W CONTINUES
TO PRODUCE STRONG UPPER E TO NE WIND FLOW ACROSS THE GULF. THE
ATMOSPHERE HERE IS SLIGHTLY MORE MOIST THAN IT WAS OVER THE PAST
FEW DAYS. SCATTERED SHOWERS ARE OVER THE SW GULF CAUSED BY
INSTABILITY NEAR THE UPPER LOW AND A NEARBY TROPICAL WAVE.
ISOLATED TO SCATTERED SHOWERS AND TSTMS ARE ALSO OVER THE SE
GULF...S FLORIDA AND CUBA TRIGGERED BY A SFC TROUGH WHICH
EXTENDS NWD FROM THE CARIB ACROSS W CUBA INTO SW FLORIDA. THE
SFC PATTERN REMAINS WEAK WITH A QUASI-STATIONARY 1014 MB HIGH
CENTER NEAR 28N93W. THIS WEAK PRES GRAD IS EXPECTED TO CONTINUE
FOR A FEW MORE DAYS ALLOWING WINDS TO REMAIN LIGHT. THE UPPER
LOW IS FORECAST TO MOVE WWD ACROSS CENTRAL MEXICO LATE TODAY.

CARIBBEAN SEA...
A CONSIDERABLE AMOUNT OF MOISTURE REMAINS OVER THE CARIBBEAN
TONIGHT. SEVERAL UPPER LEVEL FEATURES ARE ENHANCING THIS
MOISTURE. THEY ARE...THE UPPER LOW OVER THE SW GULF OF
MEXICO...TWO UPPER HIGHS NEAR 19N83W AND 14N65W AND ANOTHER
UPPER LOW NEAR THE CENTRAL BAHAMAS BAHAMAS. WITHIN THIS MOIST
UPPER ENVIRONMENT THERE ARE TWO TROPICAL WAVES AND A SFC TROUGH
HELPING TO PROVIDE EVEN MORE LIFT. SCATTERED SHOWERS AND TSTMS
ARE AFFECTING ALL THE GREATER ANTILLES. SIMILAR SHOWER ACTIVITY
IS SEEN OVER THE FAR SE CARIBBEAN AND OVER PARTS OF CENTRAL
AMERICA DUE TO THE PASSAGE OF A TROPICAL WAVE CURRENTLY LOCATED
OVER THE YUCATAN PENINSULA AND GUATEMALA. LIGHT TO MODERATE
WINDS ARE FOUND IN THE WRN PORTION OF THE BASIN AND MODERATE TO
FRESH TRADE WINDS IN THE E AND CENTRAL CARIB.

ATLANTIC OCEAN...
UPPER DIFFLUENCE BETWEEN AN UPPER LOW NEAR THE CENTRAL BAHAMAS
AND AN UPPER HIGH OVER THE E CARIB IS SUPPORTING AN AREA OF
SHOWERS AND TSTMS OVER THE SW ATLC NEAR THE SE BAHAMAS AND
HISPANIOLA. FURTHER E...AN UPPER TROUGH EXTENDS SW ACROSS THE
CENTRAL ATLC FROM AN UPPER LOW LOCATED NEAR 27N43W. RIDGING
COVERS THE REMAINDER OF THE ATLC STRETCHING W FROM AN UPPER HIGH
LOCATED NEAR MIDWAY BETWEEN THE CANARY AND CAPE VERDE ISLANDS.
THERE IS LITTLE MOISTURE ASSOCIATED WITH EITHER THE RIDGE OR
TROUGH. WV IMAGERY SHOWS ABUNDANT DRY AIR/SUBSIDENCE ALOFT E
OF 50W...ALLOWING FAIR WEATHER TO PREVAIL.

AT THE SFC...THE MAIN WEATHER FEATURE IS A STATIONARY 1025 MB
HIGH CENTERED NEAR 36N34W. THIS HIGH EXTENDS A RIDGE SW REACHING
THE NE CARIBBEAN AND THE BAHAMAS. IT IS PRODUCING LIGHT TO
MODERATE TRADES ACROSS THE BULK OF THE ATLC DISCUSSION AREA.

$$
GR



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