000
AXPZ20 KNHC 181008
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SUN NOV 18 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 
0830 UTC.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
MONSOON TROUGH EXTENDS FROM LOW PRES OVER THE SW CARIBBEAN NEAR 
11N76W 1010 MB TO 05N95W WHERE IT TRANSITIONS TO ITCZ... 
CONTINUING TO 07N113W TO 06N129W TO BEYOND 07N140W. SCATTERED 
MODERATE ISOLATED STRONG CONVECTION NOTED WITHIN 150 NM OF ITCZ 
BETWEEN 120W AND 132W.

...DISCUSSION...
ALOFT...STRONG W TO SW WINDS 75-110 KT DOMINATE MOST OF THE 
FORECAST AREA N OF 19N AND W OF 110W...DEPICTING A SUBTROPICAL 
JETSTREAM FLOWING THROUGH THE BASE OF A BROAD UPPER LEVEL TROUGH 
ACROSS THE NE PACIFIC. UPPER LEVEL RIDGING BUILDING IN BEHIND A 
SHORTWAVE SWEEPING THROUGH THE BROAD TROUGH WAS BUILDING INTO NW 
PORTIONS OF THE AREA W OF 132W THIS MORNING. THIS JET CONTINUES 
TO TRANSPORT ABUNDANT MID/UPPER LEVEL MOISTURE ACROSS THE 
FORECAST REGION FROM THE HAWAIIAN ISLANDS TO BAJA CALIFORNIA AND 
NW MEXICO. SATELLITE IMAGERY SHOWS A WIDE BAND OF TRANSVERSE 
HIGH CLOUDS IN ASSOCIATION WITH THESE STRONG WINDS. A DOWNSTREAM 
RIDGE COVERS MUCH OF THE REGION S OF 19N W OF 110W...AND IS 
CENTERED ON A WEAKENING UPPER ANTICYCLONE NEAR 15N108W THAT 
EXTENDS NE ACROSS MEXICO AND TEXAS AND INTO THE CENTRAL U.S.  A 
BROAD UPPER TROUGH EXTENDING FROM A CUT-OFF LOW LOCATED ALONG 
THE SOUTH CAROLINA COAST EXTENDS S-SW ACROSS THE EASTERN GULF OF 
MEXICO AND THE NW CARIBBEAN TO CENTRAL AMERICA NEAR 17N90W.  A 
LINGERING TUTT EXTENDS FROM A WEAK MIDDLE LEVEL VORTEX NEAR 
10N86W TO AN ELONGATED CYCLONIC VORTEX NEAR 06N112W. STRONG 
SUBSIDENCE ALONG THE N SIDE OF THIS TUTT IS LIMITING CONVECTION 
ALONG THE MONSOON TROUGH AND THE ITCZ AXIS E OF 110W.  

AT THE SURFACE...A DISSIPATING COLD FRONT ENTERS THE FORECAST 
AREA NEAR 30N118W AND EXTENDS SW TO 23N130W. A WEAK AND NARROW 
HIGH PRES RIDGE PREVAILS TO THE NW OF THE FRONT...SANDWICHED IN 
BETWEEN A SECOND COLD FRONT LOCATED N OF THE AREA ALONG 32N. THE 
WEAK RIDGE HAS SHIFTED S TO ALONG 29N AND IS INDUCING SUFFICIENT 
PRES GRADIENT N OF THE ITCZ TO FRESHEN THE TRADE WINDS TO 20-25 
KT FROM 08N TO 18N W OF 134W. EXPECT THE RIDGE TO STRENGTHEN 
SLIGHTLY DURING THE NEXT 24 HOURS...AND A NEW HIGH CENTER TO 
REFORM NEAR 29N124W BY MONDAY AFTERNOON...WHICH WILL PRODUCE A 
BROADER ZONE OF NE TO E WINDS 20-25 KT FROM 10N TO 19N W OF 124W 
AND BUILDING SEAS OF 8 TO 11 FT ACROSS THIS AREA....WITH MINOR 
CHANGE THROUGH TUESDAY. 

LONG PERIOD NW SWELL GENERATED ACROSS THE NE PACIFIC BEHIND THE 
COLD FRONTS CONTINUES TO PUSH ACROSS THE NW PART OF THE REGION 
WITH COMBINED SEAS TO 10 FT. A SECOND PULSE OF NW SWELL ENTERING 
NW PORTIONS THIS MORNING WILL CONTINUE TO PROPAGATE S AND E 
ACROSS THE REGIONAL WATERS OVER THE NEXT FEW DAY...AND COMBINE 
WITH NE WIND WAVES DEVELOPING WITHIN THE TRADE WIND ZONE TO 
PRODUCE COMBINED SEAS 8 TO 11 FT. THE NEXT PULSE OF INCREASING 
NW SWELL IS EXPECTED TO INVADE THE N WATERS EARLY TUESDAY.

A LOW LEVEL CYCLONE WAS MOVING WWD ALONG THE ITCZ...REFLECTED AT 
THE SURFACE AS AN OPEN TROUGH...ALONG 135W. A LARGE AREA OF 
SCATTERED CONVECTION OCCURRING WITH THIS FEATURE HAS BEEN LEFT 
BEHIND DUE TO INCREASING UPPER LEVEL LEVEL WIND SHEAR AND 
CONVERGENCE W OF 130W...WHILE THE CONVECTION PERSISTS BETWEEN 
120W AND 130W...IN A MORE FAVORABLE UPPER LEVEL ENVIRONMENT. 

GAP WINDS...
PERSISTENT NORTHERLY WINDS 20-30 KT CONTINUE THROUGH THE GULF OF 
TEHUANTEPEC...AS BROAD CYCLONIC LOW LEVEL FLOW ACROSS THE GULF 
OF MEXICO YIELDS MODERATE N TO NE WINDS ACROSS THE W HALF OF THE 
BASIN. WINDS EXITING THE CHIVELAS PASS CONTINUE TO BE ENHANCED 
BY NOCTURNAL DRAINAGE FLOW ACROSS THE GULF OF TEHUANTEPEC...AND 
HAVE BEEN REACHING MINIMAL GALE FORCE ROUGHLY BETWEEN 0600 AND 
1200 UTC EACH OF THE PAST FEW DAYS. THIS PATTERN AND THE INDUCED 
GAP WIND FLOW IS EXPECTED TO PERSIST FOR SEVERAL MORE DAYS. 
LATEST GLOBAL MODEL GUIDANCE SUGGESTS THAT THIS NOCTURNAL PEAK 
IN WINDS WILL INCREASE TO 40 KT EARLY MONDAY MORNING...WITH SEAS 
BUILDING TO AROUND 13 FT DOWNSTREAM OF TEHUANTEPEC. SEE LATEST 
NHC HIGH SEAS FORECAST UNDER AWIPS/WMO HEADERS HSFEP2/FZPN03 
KNHC FOR DETAILS ON THESE FLUCTUATING WINDS. 

PULSING OF NOCTURNAL WINDS ARE ALSO EXPECTED ACROSS THE GULF OF 
PAPAGAYO..WITH NOCTURNAL WINDS FORECAST TO REACH AROUND 20 KT 
FROM 0600 TO 1200 UTC...WITH SEAS OF 6-7 FT THROUGH AND DOWNWIND 
OF THE GULF.  

$$
STRIPLING