000
AXPZ20 KNHC 310927
TWDEP 

TROPICAL WEATHER DISCUSSION  
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC WED OCT 31 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0900 UTC.

...SPECIAL FEATURE...

TROPICAL STORM ROSA CENTERED NEAR 14.5N 117.3W AT 31/0900 UTC 
MOVING W OR 275 DEGREES AT 4 KT. ESTIMATED MINIMUM CENTRAL 
PRESSURE IS 1003 MB. MAXIMUM SUSTAINED WINDS ARE 40 KT GUSTS TO 
50 KT. WESTERLY SHEAR IS DISPLACING THE CONVECTION EAST OF THE 
LOW-LEVEL CENTER. AS A RESULT...SATELLITE IMAGERY SHOWS NUMEROUS 
MODERATE ISOLATED STRONG CONVECTION WITHIN 180 NM E SEMICIRCLE 
OF ROSA. SCATTERED MODERATE CONVECTION IS ELSEWHERE FROM 13N TO 
16N BETWEEN 112W AND 118W. A PARTIAL ASCAT PASS AT 0434 UTC 
REVEALED A BAND OF 35-40 KT WINDS WITHIN THE EASTERN SEMICIRCLE. 
SOME STRENGTHENING IS POSSIBLE TODAY WITH ROSA REACHING PEAK 
INTENSITY OF 45 KT GUSTS TO 55 KT THIS AFTERNOON...FOLLOWED BY 
SLOW WEAKENING ON THURSDAY. ROSA IS FORECAST TO MOVE VERY LITTLE 
DURING THE NEXT FEW DAYS...AND COULD BECOME NEARLY STATIONARY BY 
THURSDAY NIGHT. SEE LATEST NHC FORECAST/ ADVISORY UNDER AWIPS/ 
WMO HEADERS MIATCMEP2/WTPZ22 KNHC FOR MORE DETAILS.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...

MONSOON TROUGH EXTENDS FROM 07N78W TO LOW PRES NEAR 09N87W 1010 
MB TO 11N104W. ITCZ AXIS STRETCHES FROM LOW PRES NEAR 14N125W 
1011 MB TO LOW PRES NEAR 11N132W 1009 MB TO BEYOND 08N140W. NO 
DEEP CONVECTION.

...DISCUSSION...

ALOFT...A RIDGE/TROUGH/RIDGE PATTERN DOMINATES THE FORECAST 
REGION. AN UPPER-LEVEL TROUGH ENTERS THE AREA NEAR 30N124W THEN 
CONTINUES SW BEYOND 24N140W. THE TROUGH AXIS CROSSES JUST E OF 
THE HAWAIIAN ISLANDS. A RIDGE IS BUILDING BEHIND THE TROUGH AXIS 
OVER THE NW CORNER OF THE FORECAST AREA. AN ANTICYCLONIC 
CIRCULATION CENTERED NEAR 14N125W HAS A RIDGE EXTENDING NE 
ACROSS BAJA CALIFORNIA AND NW MEXICO INTO THE SW CONUS. THIS 
BROAD SYSTEM COVERS THE MAJORITY OF THE DISCUSSION AREA...AND IS 
PRODUCING STRONG NW WINDS OVER A WEAK LOW PRES LOCATED NEAR 
15N108W. THIS SYSTEM CONTINUES TO PRODUCE DISORGANIZED SHOWER 
AND THUNDERSTORM ACTIVITY. UPPER-LEVEL WINDS ARE NOT CONDUCIVE 
FOR SIGNIFICANT DEVELOPMENT...AND IT HAS A LOW CHANCE OF 
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT 
DRIFTS WESTWARD. NUMEROUS MODERATE ISOLATED STRONG CONVECTION IS 
NOTED WITHIN 120 NM E SEMICIRCLE OF LOW CENTER. 

AT THE SURFACE...A 1019 MB HIGH PRES CENTER IS ANALYZED AT 
29N126 WITH A RIDGE EXTENDING SE TO NEAR 24N112W. NE TRADE WINDS 
OF 15-20 KT ARE SEEN ON THE SOUTHERN PERIPHERY OF THE RIDGE PER 
THE MOST RECENT SCATTEROMETER PASSES. THE HIGH PRES WILL REMAIN 
NEARLY STATIONARY OVER THE N WATERS DURING THE NEXT COUPLE OF 
DAYS...WITH A BELT OF NE TO E WINDS IN THE 15-20 KT RANGE 
PERSISTING MAINLY FROM 15N TO 20N W OF 120W.  

A COLD FRONT IS CURRENTLY MOVING ACROSS THE FAR NW CORNER OF THE 
FORECAST WATERS...AND IS EXPECTED TO REACH A POSITION FROM 
30N131W TO 26N140W LATE TONIGHT WHILE WEAKENING. NW SWELL IN THE 
WAKE OF THE FRONT WILL RAISE SEAS TO 9 FT.

THE PAIR OF WEAK LOW PRES SYSTEMS PREVIOUSLY DESCRIBED ALONG THE 
ITCZ AXIS ARE WELL DEFINED ON SATELLITE IMAGERY WHERE A COUPLE 
OF SWIRLS OF LOW CLOUDS ARE NOTED. 

GAP WINDS...
ACCORDING TO THE MOST RECENT SCATTEROMETER PASS...WINDS HAVE 
DIMINISHED TO 20 KT OR LESS IN THE GULF OF TEHUANTEPEC.  

WINDS IN THE GULF OF PAPAGAYO WILL LIKELY INCREASE TO 20-25 KT 
THIS MORNING AND THU MORNING AS A BROAD AREA OF LOW PRES 
DEVELOPS OVER THE SW CARIBBEAN. 

$$
GR