000
AXPZ20 KNHC 230305
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC SUN SEP 23 2012

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS 
BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND 
METEOROLOGICAL ANALYSIS.

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0300 UTC.

...SPECIAL FEATURES...
TROPICAL STORM MIRIAM AT 14.9N 108.5W 1002 MB AT 0300 UTC SEP 23 
MOVE W-NW OR 300 DEG AT 8 KT. MAXIMUM SUSTAINED WIND 40 GUSTS 
50 KT. BANDING ORGANIZATION AROUND ITS CENTER HAS IMPROVED WITH 
WELL DEVELOPED UPPER LEVEL OUTFLOW. MIRIAM REMAINS OVER WARM 
SST AND LOW WIND SHEAR ALOFT WHICH ALLOWS IT TO CONTINUE ITS 
INTENSIFICATION. MIRIAM EXPECTED TO BECOME A HURRICANE LATE SUN 
NIGHT. ITS NW TRACK WILL BRING MIRIAM INTO COLDER WATERS AND 
INCREASED SOUTHERLY SHEAR BY MON NIGHT...WEAKENING AND TURNING 
IN A MORE NORTHERLY TRACK. SCATTERED MODERATE TO STRONG 
CONVECTION CURRENTLY WITHIN 240 NM N AND 180 NM S SEMICIRCLES 
EXPECTED TO EXPAND IN INTENSITY AND COVERAGE THROUGH MON. SEE 
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP3/ 
WTPZ23 KNHC FOR MORE DETAILS. 

...TROPICAL WAVES...
SCATTERED MODERATE TO STRONG CONVECTION SHIFTING WWD ACROSS THE 
TROPICAL EPAC APPEARS TO BE IN SYNC WITH A TROPICAL WAVE ACROSS 
THE YUCATAN PENINSULA...AND IS ASSUMED TO BE THE SOUTHERN 
PORTION OF THIS WAVE....CENTERED ALONG ABOUT 90W...AND MOVING W 
10-15 KT. THE WAVE HAS PERTURBED THE MONSOON TROUGH AND A WAVE 
OR UNDULATION IN THE TROUGH WAS EVIDENT IN OVERNIGHT 
SCATTEROMETER PASSES. THIS SOUTHERN PORTION OF THE WAVE WILL 
BREAK AWAY FROM THE REST OF THE WAVE ACROSS CENTRAL AMERICA IN 
THE NEXT 24 HOURS...AND CONTINUE TO SHIFT WWD. 

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
MONSOON TROUGH EXTENDS FROM 10N86W TO 10N96W TO 12N101W THEN 
RESUMES FROM 12N110W TO 09N130W THEN ITCZ 09N136W TO BEYOND 
09N140W. SCATTERED MODERATE ISOLATED STRONG CONVECTION WITHIN 
180 NM S AND 90 NM N OF TROUGH AXIS FROM 90W TO 100W. SCATTERED 
MODERATE ISOLATED STRONG CONVECTION WITHIN 120 NM OF ITCZ AXIS W 
OF 133W.

...DISCUSSION...
ALOFT...UPPER LEVEL TROUGH EXTENDS FROM 32N125W TO BEYOND 
32N140W HAS 2 DEGREE SWATH OF TROPICAL MOISTURE JUST S OF AXIS 
HEADING TO SOUTHERN CALIFORNIA RIDING ON 60 KT JET CORE. NARROW 
FLATTENED RIDGE CREST AND A WEAK CYCLONE AT 22N125W WITH TROUGH 
ALOFT TO SOUTHERN TIP OF BAJA CALIFORNIA MAINTAIN DRY AND STABLE 
SUBSIDING AIR MASS ELSEWHERE W OF 121W AND N OF 20N E OF SWATH 
OF MOISTURE. BROAD UPPER LEVEL ANTICYCLONE AT 15N100W RIGHT 
NEXT TO TROPICAL STORM MIRIAM MAINTAINS LIGHT SHEAR WINDS AND 
GOOD DIVERGENT OUTFLOW FOR MIRIAM.

AT LOWER LEVELS...HIGH PRES CENTER 1023 MB AT 35N135W EXTENDS 
RIDGE ACROSS N WATERS TO 20N115W. AREA OF FRESH TRADE WINDS ON 
SOUTHEASTERN PERIPHERY OF RIDGE FROM 10N TO 15N W OF 133W. 
TRADES EXPECTED TO DIMINISH WITHIN 24 HOURS AS HIGH PRES WEAKENS 
AND COLD FRONT MOVES CLOSER THEN STALLS IN NW PORTION OF BASIN. 
NW SWELL GENERATED BEHIND FRONT WILL BUILD SEAS TO 11 FT ACROSS 
W PARTS OF E PAC. 

GAP WINDS...GULF OF TEHUANTEPEC GAP WINDS EXPECTED TO CONTINUE 
UNABATED THROUGH FORECAST PERIOD WITH SEAS BUILDING TO 9 FT. 

$$
WALLY BARNES