000
AXPZ20 KNHC 231555
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC WED SEP 23 2009

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

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1500 UTC.

...SPECIAL FEATURE...

TROPICAL STORM NORA IS NEAR 16.5N 117.5W AT 23/1500 UTC MOVING 
W-NW OR 300 DEG AT 8 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 
1002 MB. MAXIMUM SUSTAINED WIND SPEED IS 40 KT WITH GUSTS TO 50 
KT. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS 
MIATCMEP2/WTPZ22 KNHC FOR MORE DETAILS. NORA HAS BECOME A LITTLE 
BETTER ORGANIZED THIS MORNING...AS A CENTRAL CONVECTIVE FEATURE 
HAS FORMED WITH AN OUTER BAND...WITH NUMEROUS MODERATE TO STRONG 
CONVECTION...IN THE WESTERN SEMICIRCLE. NORA APPEARS TO HAVE 
ABOUT 24 HOURS OR SO TO STRENGTHEN BEFORE SHEAR INCREASES FROM 
THE SOUTHWEST OR WEST DUE TO A LARGE EASTERN PACIFIC TROUGH... 
AND THE CYCLONE REACHES COOLER SEA SURFACE TEMPERATURES. 

...THE ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE IS ALONG 09N79W TO 08N100W TO 
13N112W THEN CONTINUING FROM 13N120W TO 08N140W. SCATTERED 
MODERATE CONVECTION IS WITHIN 80 NM EITHER SIDE OF AXIS E OF 
92W...AND WITHIN 120 NM BETWEEN 102W AND 110W. A CLUSTER OF 
MODERATE TO ISOLATED STRONG CONVECTION IS WITHIN 80 NM OF 
10.5N126W. SIMILAR CONVECTION CAN BE FOUND FROM 04N TO 13N W OF 
134W. 

...DISCUSSION...

WEAK HIGH PRES AND MOSTLY BROKEN STRATOCUMULUS CLOUDS DOMINATE 
THE N WATERS...PARTICULARLY N OF 20N AND JUST W OF THE BAJA 
CALIFORNIA PENINSULA. A SURFACE TROUGH...REMNANTS OF FORMER 
TROPICAL STORM MARTY LIES ALONG 136W FROM 22N TO 27N. AN EARLIER 
ASCAT PASS SHOWED NE TO E WINDS OF 15 TO 20 KT ASSOCIATED WITH 
THIS TROUGH. THIS AREA OF WINDS IS EXPECTED TO MIGRATE SW AS THE 
RIDGE AXIS SWEEPS SOUTHWESTWARD AND THE WEAKENING TROUGH 
APPROACHES 140W. A COLD FRONT...IN ASSOCIATION WITH A DEEP LAYER 
TROUGH...IS APPROACHING THE FAR NW CORNER OF THE AREA BUT IS 
FORECAST TO WEAKEN BEFORE MOVING INTO THE FORECAST REGION. A 
COLD FRONT IS MOVING ACROSS THE NW PORTION OF THE GULF OF 
MEXICO. HIGH PRES BEHIND IT IS PRODUCING 15 KT NLY WINDS OVER 
THE NORTHERN PORTION OF THE GULF OF CALIFORNIA...EXPECTED TO 
INCREASE TO 20 KT LATER TODAY AS A SECONDARY WIND SURGE PASSES S 
INTO NW MEXICO. 

ANOTHER SURFACE TROUGH EXTENDS FROM 15N133W TO 06N135W. 
CONVECTION IS INCREASING NEAR AND AHEAD OF THE TROUGH AXIS AND 
COVERS THE AREA FROM 04N TO 13N W OF 134W. A DIFFLUENT PATTERN 
ALOFT ASSOCIATED WITH AN UPPER LEVEL ANTICYCLONE CENTERED NEAR 
14N138W IS HELPING TO INDUCE THIS CONVECTIVE ACTIVITY. 

A WELL PRONOUNCED MID/UPPER ANTICYCLONE CENTERED OVER INLAND 
MEXICO NEAR 22N100W EXTENDS A RIDGE SW TO JUST EAST OF TROPICAL 
STORM NORA. A BROADLY DIFFLUENT UPPER LEVEL PATTERN ASSOCIATED 
WITH THIS FEATURE IS SUPPORTING A 120 NM WIDE BAND OF MODERATE 
TO ISOLATED STRONG CONVECTION ALONG THE PACIFIC COAST OF MEXICO 
BETWEEN ZIHUATANEJO AND PUERTO VALLARTA. 

GAP WINDS...
THE COLD FRONT PASSING SOUTH THROUGH THE WESTERN GULF OF MEXICO 
IS EXPECTED TO BRING 20 KT NORTHERLY FLOW THROUGH THE BAY OF 
CAMPECHE INTO THE GULF OF TEHUANTEPEC OVERNIGHT TONIGHT AND 
CONTINUE THROUGH THE FORECAST PERIOD.

$$
GR