000
AXPZ20 KNHC 071622
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SUN OCT 07 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1500 UTC.

...SPECIAL FEATURE...

TROPICAL STORM OLIVIA NEAR 14.5N 121.0W 998 MB AT 1500 UTC OCT 
07 MOVING NW OR 305 DEG AT 5 KT. MAXIMUM SUSTAINED WINDS 50 KT 
GUSTS 60 KT. CONVECTION ASSOCIATED WITH OLIVIA HAS CONTINUED TO 
REMAIN CONCENTRATED SURROUNDING THE CENTER....WITH SCATTERED TO 
NUMEROUS MODERATE TO STRONG CONVECTION OCCURRING WITHIN 120 NM 
OF THE CENTER. REMAINING CONVECTION WAS SCATTERED ABOUT A NE TO 
SW AXIS...EXTENDING SEVERAL HUNDRED MILES TO THE SW WHERE IT 
MERGED WITH CONVECTION ALONG THE MONSOON TROUGH. ALTHOUGH 
OVERNIGHT SCATTEROMETER DATA SUGGESTED THE CENTER TO BE WELL SW 
OF THE CURRENT POSITION...RECENT MICROWAVE IMAGERY WAS DEFINITE 
IN PLACING THE CENTER NEAR THE MIDDLE LEVEL CENTER SEEN IN IR 
SATELLITE IMAGERY OVERNIGHT. HOWEVER...THE SAME MICROWAVE 
IMAGERY SUGGESTS THAT SOUTHWESTERLY VERTICAL WIND SHEAR IS 
TILTING THE SYSTEM...WITH THE SURFACE CENTER ABOUT 30 NM TO THE 
SW OF THE MIDDLE LEVEL CENTER. SOME STRENGTHENING OF OLIVIA IS 
POSSIBLE DURING THE NEXT 24-36 HOURS AS IT CONTINUES ON A SLOW 
NW TRACK...BUT THE VERTICAL WIND SHEAR IS EXPECTED TO INCREASE 
SIGNIFICANTLY BY 48 HOURS AND BEGIN TO WEAKEN...AND POSSIBLY 
DECOUPLE THE LOW LEVEL CENTER FROM THE MIDDLE LEVEL CIRCULATION. 
IF THIS IS TO OCCUR...THE LOW LEVEL CENTER WILL THEN LIKELY MOVE 
WSW IN THE PREVAILING LOW LEVEL WIND FLOW. OLIVIA IS NO LONGER 
FORECAST TO BECOME A HURRICANE. FOR FURTHER DETAILS SEE THE 
LATEST FORECASTS UNDER AWIPS/WMO HEADERS MIATCMEP5 AND WTPZ25 
KNHC.  

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

MONSOON TROUGH EXTENDS FROM 09N85W TO 09N99W TO 11N111W WHERE IT 
ENDS. IT RESUMES SW OF TROPICAL STORM OLIVIA AT 11N124W TO 
08N134W WHERE IT TRANSITIONS TO THE ITCZ AXIS TO 09N140W. 
SCATTERED MODERATE ISOLATED STRONG WITHIN 120 NM S OF THE TROUGH
BETWEEN 85W AND 90W AND WITHIN 60 NM OF THE TROUGH W OF 124W.

...DISCUSSION...

A VERY BROAD UPPER LEVEL BLOCKING PATTERN PERSISTS TODAY ACROSS 
THE REGION BETWEEN 50W AND 145W. TROPICAL STORM OLIVIA REMAINS 
UNDERNEATH A BROAD UPPER LEVEL RIDGE THAT IS N OF 10N BETWEEN 
105W AND 130W...WITH TWO UPPER LEVEL ANTICYCLONES ON EITHER SIDE 
OF OLIVIA...TO THE E AND TO THE NW. A VERY SHARP AND ENERGETIC 
UPPER LEVEL TROUGH ACROSS THE CENTRAL PACIFIC N OF THE HAWAIIAN 
ISLANDS IS BECOMING INCREASINGLY NEGATIVELY TILTED...AND HAS 
HELPED TO EJECT SEVERAL SHORTWAVES FROM THE CENTRAL TROPICAL 
PACIFIC NE AVER THE ABOVE RIDGE...WHICH HAS ACTED TO SHIFT ITS 
CREST TO THE NE OF THE PARENT ANTICYCLONES. THIS PROCESS WILL 
EVENTUALLY ERODE THE N PORTIONS OF THE RIDGE TUE AND WED...AND 
FLATTEN THE RIDGE TO S OF 28-30N. AN UPPER TROUGH EXTENDS FROM 
THE CENTRAL U.S. SW TO ACROSS THE WESTERN GULF OF MEXICO...AND 
TO OVER CENTRAL MEXICO TO NEAR 14N98W. MOIST NORTHERLY LLVL WIND 
FLOW SPILLING FROM THE GULF OF MEXICO THROUGH THE GULF OF 
TEHUANTEPEC IS ACTING TO IGNITE SCATTERED SMALL CELLS OF 
MODERATE CONVECTION IN THE FAVORABLE UPPER ENVIRONMENT E OF THIS 
UPPER TROUGH. AN UPPER LEVEL ANTICYCLONE RESIDES OVER THE W 
CARIBBEAN TO THE SE OF THIS UPPER TROUGH...WITH MILD E TO SE 
FLOW FOUND TO ITS S...ACROSS CENTRAL AMERICA AND THE FAR SE 
WATERS. DEEP CONVECTION ALONG THE MONSOON TROUGH E OF 90W IS 
ACTING TO DIVERT THIS UPPER FLOW AND INDUCING STRONG UPPER 
DIVERGENCE FOR SUSTAINED ACTIVE CONVECTION NEAR THE MONSOON 
TROUGH E OF 90W.

ELSEWHERE AT THE LOW LEVELS...A WEAK SURFACE HIGH PRESSURE OF 
1018 MB IS ANALYZED AT 30N130W WITH RIDGING COVERING THE 
DISCUSSION AREA N OF 20N W OF THE BAJA PENINSULA. NW WINDS OF 
20-25 KT ARE PRESENT IN THE FAR NE PART OF THE AREA N OF 27.5N E 
OF 117.5W TO THE NORTHERN BAJA CALIFORNIA PENINSULA DUE TO THE 
PRES GRADIENT BETWEEN THE RIDGE AND THE GULF OF CALIFORNIA 
THERMAL TROUGH. SEAS ACROSS THIS ZONE WERE RUNNING 6-8 FT. THE 
GRADIENT WILL RELAX BY MON AFTERNOON ALLOWING FOR THESE WINDS TO 
DIMINISH TO 20 KT OR LESS INTO TUE WITH SEAS SUBSIDING TO 6-7 FT 
ON MON AND INTO TUE. 

GAP WINDS...N TO NE WINDS OF 20-25 KT ARE EXPECTED TO CONTINUE 
TO PULSE THROUGH THE GULF OF TEHUANTEPEC THROUGH THE MIDDLE OF 
NEXT WEEK...INCREASING TO 20-30 KT ON THU. THE STRONGEST 
DRAINAGE FLOW WILL OCCUR LATE EACH NIGHT THROUGH A COUPLE OF 
HOURS AFTER DAYBREAK EACH MORNING.  

ELONGATED CYCLONIC TURNING OCCURRING ALONG THE MONSOON TROUGH 
FROM THE SW CARIBBEAN INTO THE FAR EPAC E OF 90W WILL INTERACT 
WITH A WEAK TROPICAL WAVE CURRENTLY ACROSS THE SW CARIBBEAN... 
AND IS EXPECTED TO PRODUCE A BROAD LOW PRESSURE CENTER ALONG THE 
MONSOON TROUGH NEAR 90W BY TUE. ACTIVE CONVECTION AND SW WINDS 
AROUND 20 KT ARE EXPECTED TO PERSIST ACROSS THIS REGION S OF 10N 
AND E OF 95W THROUGH TUE OR WED. 
 
$$
STRIPLING