000
AXPZ20 KNHC 222205
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC SAT SEP 22 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2100 UTC.

...SPECIAL FEATURES...
TROPICAL STORM MIRIAM AT 14.3N 107.8W 1003 MB AT 2100 UTC SEP 
22 MOVE W-NW OR 300 DEG AT 8 KT.  MAXIMUM SUSTAINED WIND 35 
GUSTS 45 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 OR SUN NIGHT.  ITS NW TRACK WILL BRING MIRIAM 
INTO COLDER WATERS AND INCREASED SOUTHERLY SHEAR BY MON NIGHT... 
WEAKENING IT AND TURNING MORE NORTHERLY TRACK.  SCATTERED 
MODERATE TO STRONG CONVECTION CURRENTLY WITHIN 180 NM N AND 120 
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 10N84W TO 08N887W TO 10N94W TO 
09N97W TO 12N101W THEN RESUMES FROM 15N116W TO 09N129W THEN ITCZ 
08N134W TO 09N138W TO BEYOND 08N140W.  SCATTERED MODERATE 
ISOLATED STRONG CONVECTION WITHIN 180 NM S AND 90 NM N OF TROUGH 
AXIS FROM 88W TO 100W.  SCATTERED MODERATE ISOLATED STRONG 
CONVECTION WITHIN 90 NM OF ITCZ AXIS W OF 133W.

...DISCUSSION...
ALOFT...UPPER LEVEL TROUGH EXTENDS FROM 32N125W TO 28N140W WITH 
2 DEGREE SWATH OF TROPICAL MOISTURE AHEAD OF AXIS HEADING TO 
SOUTHERN CALIFORNIA RIDING ON 70 KT JET CORE.  NARROW TILTED 
RIDGE CREST AND WEAK CYCLONE 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 RIGHT NEXT TO TROPICAL STORM MIRIAM 
MAINTAINS LIGHT SHEAR WINDS AND GOOD DIVERGENT OUTFLOW FOR 
MIRIAM.

AT LOWER LEVELS...HIGH PRES CENTER 1026 MB AT 37N134W 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