000
AXPZ20 KNHC 190950
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SAT SEP 19 2009

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN
FROM THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0745 UTC.

...SPECIAL FEATURES...

AT 19/0300 UTC...TROPICAL STORM MARTY IS LOCATED NEAR 22.2N 
116.8W MOVING W-NW OR 295 DEG AT 8 KT. MAXIMUM SUSTAINED WIND 
SPEED IS 30 KT WITH GUSTS TO 40 KT. ESTIMATED MINIMUM CENTRAL 
PRESSURE IS 1005 MB. INFRARED SATELLITE IMAGERY SHOWS A 
SIGNIFICANT DECREASE IN DEEP CONVECTION ASSOCIATED WITH THE 
SYSTEM...WITH ONLY SCATTERED MODERATE CONVECTION NOTED WITHIN 60 
NM SW QUADRANT OF TROPICAL DEPRESSION MARTY. THE CYCLONE IS 
FORECAST TO DEGENERATE INTO A REMNANT LOW WITHIN THE NEXT 24 
HOURS AS IT ENCOUNTERS STRONGER VERTICAL WIND SHEAR...DRIER 
AIR...AND COOLER WATERS. SEE LATEST NHC FORECAST/ADVISORY UNDER 
AWIPS/WMO HEADERS MIATCMEP1/WTPZ21KNHC FOR MORE DETAILS. 

A 1006 MB LOW PRESSURE SYSTEM IS CENTERED NEAR 19N108W...ABOUT 
170 MILES WEST OF MANZANILLO...MOVING NW TO NW NEAR 10 KT. 
CONVECTION CONTINUES TO INCREASE IN INTENSITY NEAR THE 
LOW...WITH NUMEROUS MODERATE TO STRONG CONVECTION NOTED IN 
INFRARED IMAGERY FROM GOES-12 AT 0745 UTC WITHIN 60 NM OF THE 
LOW AND SCATTERED MODERATE ELSEWHERE WITHIN 150 NM S QUADRANT OF 
LOW. ENVIRONMENTAL CONDITIONS APPEAR FAVORABLE FOR ADDITIONAL 
DEVELOPMENT...AND A TROPICAL DEPRESSION COULD FORM AT ANY TIME 
DURING NEXT DAY OR TWO. THERE IS A HIGH CHANCE...GREATER THAN 50 
PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE 
NEXT 48 HOURS.

...TROPICAL WAVE...

A TROPICAL WAVE IS ALONG 92W N OF 09N MOVING W 15 KT. THE WAVE 
IS POOLING MOSITURE IN AN AREA OF UPPER LEVEL DIFFLUENCE 
BETWEEN A LOW OVER THE WESTERN CARIBBEAN NEAR 14N80W AND AN 
ANTICYCLONE CENTERED OVER MEXICO NEAR 20N99W. AS A 
RESULT...SCATTERED MODERATE WITH ISOLATED STRONG CONVECTION CAN 
BE FOUND NEAR THE WAVE WITHIN 120 NM S OF THE COAST OF CENTRAL 
AMERICA FROM 86W TO 100W. 

...THE ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE LIES ALONG A LINE FROM 08N77W 
TO 11N93W TO 09N105W TO 11N125W TO 09N140W. SCATTERED MODERATE 
WITH ISOLATED STRONG CONVECTION CAN BE FOUND WITHIN 240 NM S OF 
THE ITCZ AXIS BETWEEN 106W TO 110W. SCATTERED MODERATE 
CONVECTION LIES WITHIN 90 NM N OF THE ITCZ AXIS BETWEEN 117W AND 
123W AND WITHIN 90 NM N AND 60 NM S OF THE ITCZ AXIS BETWEEN 
127W AND 136W.

...DISCUSSION...

W OF 120W...SURFACE RIDING ASSOCIATED WITH A 1022 MB HIGH PRES 
CENTER NEAR 33N128W DOMINATES THE PATTERN N OF 15N AND W OF 
120W. THIS RIDGING HAS WEAKENED OVER THE LAST 24 HOURS AS A DEEP 
LAYER TROUGH HAS MOVED THROUGH THE NORTHEAST PACIFIC WITH ITS 
ASSOCIATED COLD FRONT CURRENTLY APPROACHING THE PACIFIC NW 
UNITED STATES. NW SWELL ASSOCIATED WITH THIS SYSTEM WILL BEGIN 
TO SUBSIDE OVER N CENTRAL WATERS TODAY. A NEW BATCH OF NW SWELL 
ORIGINATING FROM THE SYSTEM CURRENTLY N OF HAWAII SHOULD MOVE 
INTO NW WATERS SUN...SHIFTING THE AREA OF SEAS TO 8 FT FARTHER 
W. THE 0402 QUIKSCAT PASS SHOWED TRADE WINDS STILL TO 20 KT OVER 
W WATERS FROM 13N TO 21N W OF 135W AS WELL AS N TO NE WINDS OVER 
N CENTRAL WATERS WHERE THE PRES GRADIENT TIGHTENS ZONALLY 
BETWEEN THE HIGH AND LOWER PRES OVER THE GULF OF 
CALIFORNIA...T.D. MARTY...AND THE AFOREMENTIONED LOW. THESE 
WINDS WILL DIMINISH BELOW 20 KT ON SUNDAY AS THE HIGH PRES TO 
THE N WEAKENS...WEAKENING THE RIDGING OVER THIS AREA. FARTHER 
S...CONVECTION ALONG THE ITCZ IS BEING SPURRED ON BY BROAD UPPER 
LEVEL DIFFLUENCE BETWEEN 
AN ANTICYCLONE CENTERED NEAR 13N135W AND A LOW NEAR 03N123W.

E OF 120W...DEEP SOUTHERLY FLOW BETWEEN 100W AND 115W IS 
TRANSPORTING TROPICAL MOISTURE NORTHWARD INTO THE BROAD AREA OF 
SURFACE TROUGHING SUPPORTING BOTH T.D. MARTY AND THE LOW PRES 
SYSTEM MENTIONED IN THE SPECIAL FEATURES SECTION. THIS BROAD 
TROUGHING IS FORECAST TO MOVE W AND ALLOW THE HIGH PRES RIDGE TO 
INFILTRATE THE N PORTION OF THE REGION AS T.D. MARTY DISSIPATES. 
EXPECT CONDITIONS TO BECOME INCREASINGLY SUBSIDENT HERE BY THE 
END OF THE FORECAST PERIOD AS A RESULT. FOR NOW...SATELLITE 
PRECIPITABLE WATER IMAGERY SHOWS A SURGE OF MOISTURE MOVING N 
THROUGH THE GULF OF CALIFORNIA WHICH WILL LIKELY ENHANCE MONSOON 
THUNDERSTORMS OVER THE SIERRA MADRE OCCIDENTAL AND PORTIONS OF 
THE DESERT SW. FARTHER S...THE PREVIOUSLY MENTIONED TROPICAL 
WAVE IS DRIVING MOST OF THE SENSIBLE WEATHER. MEANWHILE...THE SW 
SWELL EVENT WITH PERIODS IN THE 14-16 SECOND RANGE CONTINUES ON 
THE PACIFIC COASTS OF MEXICO AND CENTRAL AMERICA. WAVE WATCH 
GUIDANCE SHOWS A NEW SLY SWELL TRAIN WITH LEADING PERIODS OF 
17-19 SECONDS REACHING THE COASTLINE BY SUN.

$$
SCHAUER CLARK