000
AXPZ20 KNHC 232154
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC WED SEP 23 2009

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

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2115 UTC.

...SPECIAL FEATURE...

TROPICAL STORM NORA IS NEAR 16.8N 118.6W AT 23/2100 UTC MOVING 
W-NW OR 290 DEG AT 6 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 
1000 MB. MAXIMUM SUSTAINED WIND SPEED HAS INCREASED TO 45 KT 
WITH GUSTS TO 55 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER 
AWIPS/WMO HEADERS MIATCMEP2/WTPZ22 KNHC FOR MORE DETAILS. NORA 
CONTINUES TO STRENGTHEN WITH A WELL DEFINED CYCLONICALLY-CURVED 
CONVECTIVE BAND WRAPPING AROUND A SMALL CENTRAL DENSE 
OVERCAST...AND FAIR OUTFLOW IN ALL DIRECTIONS. THE CYCLONE 
APPEARS TO HAVE A DAY OR TWO TO INTENSIFY BEFORE SHEAR INCREASES 
FROM THE SOUTHWEST OR WEST DUE TO A LARGE EASTERN PACIFIC 
TROUGH...AND NORA REACHES COOLER SEA SURFACE TEMPERATURES. THE 
OFFICIAL INTENSITY FORECAST KEEPS NORA AS A TROPICAL STORM 
DURING THE NEXT 48 HOURS...AND IT IS NOT OUT OF THE QUESTION 
THAT THIS TROPICAL SYSTEM MAY REACH HURRICANE FORCE WINDS.

...THE ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE IS ALONG 09N79W TO 09N92W TO 
09N101W TO 14N116W TO 09N130W TO 08N140W. SCATTERED MODERATE 
ISOLATED STRONG WITHIN 180 NM S OF AXIS BETWEEN 105W AND 111W 
AND 120 NM S OF AXIS BETWEEN 126W AND 131W. SCATTERED MODERATE 
WITHIN 120 NM S OF AXIS BETWEEN 83W AND 89W AND 102W AND 105W. 

...DISCUSSION...

A 1021 MB HIGH LOCATED NEAR 33N130W EXTENDS A RIDGE OVER 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 138W FROM 20N TO 27N. A WEAKENING SWIRL OF LOW 
CLOUDS IS ASSOCIATED WITH THIS FEATURE. AN EARLIER QSCAT PASS 
ALSO SHOWED NE TO E WINDS OF 15 TO 20 KT ON EITHER SIDE OF THE 
TROUGH AXIS. THIS AREA OF WINDS WILL MOVE WWD IN TANDEM WITH THE 
TROUGH EXPECTED TO REACH 140W THU MORNING. 

THE FIRST COLD FRONT OF THIS FALL SEASON IS MOVING SLOWLY SE 
ACROSS THE WESTERN GULF OF MEXICO. HIGH PRES BEHIND IT IS 
PRODUCING 20 KT NLY WINDS OVER THE NORTHERN PORTION OF THE GULF 
OF CALIFORNIA. THIS WILL BE A SHORT-LIVED EVENT AND WINDS ARE 
EXPECTED TO DIMINISH TO BELOW 20 KT IN ABOUT 24 TO 30 HOURS. THE 
SAME FRONTAL SYSTEM IS EXPECTED TO BRING 20 TO 25 KT NORTHERLY 
FLOW THROUGH THE BAY OF CAMPECHE INTO THE GULF OF TEHUANTEPEC 
OVERNIGHT TONIGHT AND CONTINUE THROUGH THE FORECAST PERIOD.

ANOTHER SURFACE TROUGH IS ALONG 130W FROM O6N TO 14N. CONVECTION 
NEAR AND AHEAD OF THE TROUGH AXIS HAS DIMINISHED SINCE THIS 
MORNING. VIS SATELLITE IMAGERY INDICATES SOME CYCLONIC TURNING 
NEAR THE INTERSECTION OF THE TROUGH AXIS AND THE ITCZ. SCATTERED 
SHOWERS AND ISOLATED TSTMS ARE WITHIN 180 NM EITHER SIDE OF THE 
TROUGH AXIS. A DIFFLUENT PATTERN ALOFT ASSOCIATED WITH AN UPPER 
LEVEL ANTICYCLONE CENTERED NEAR 14N138W IS HELPING TO INDUCE THE 
CONVECTIVE ACTIVITY ASSOCIATED WITH THIS TROUGH.

A WELL PRONOUNCED MID/UPPER ANTICYCLONE CENTERED OVER INLAND 
MEXICO NEAR TAMPICO EXTENDS A RIDGE SW TO JUST EAST OF TROPICAL 
STORM NORA. A BROADLY DIFFLUENT UPPER LEVEL PATTERN ASSOCIATED 
WITH THIS FEATURE IS SUPPORTING A CLUSTER OF MODERATE TO 
ISOLATED STRONG CONVECTION ALONG THE PACIFIC COAST OF MEXICO 
BETWEEN 104W AND 106W. THIS ANTICYCLONE IS ALSO ENHANCING 
CONVECTION ALONG THE COASTLINE OF CENTRAL AMERICA AND NEAR THE 
ITCZ. 

$$
GR