000
AXPZ20 KNHC 270920
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC FRI OCT 26 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 
0845 UTC.

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

MONSOON TROUGH EXTENDS FROM 11N86W TO LOW PRES NEAR 10N96W 1008 
MB TO LOW PRES NEAR 11N107W 1008 MB TO LOW PRES NEAR 11N121W 
1008MB TO 08N140W. SCATTERED MODERATE TO STRONG CONVECTION IS 
NOTED WITHIN 150 NM NE QUADRANT OF SECOND LOW PRES. SCATTERED 
MODERATE ISOLATED STRONG CONVECTION IS MAINLY ON THE WEST SIDE 
OF LOW PRES NEAR 11N121W COVERING THE AREA FROM 10N TO 12.5N 
BETWEEN 121W AND 127W. SCATTERED MODERATE CONVECTION IS SEEN 
FROM 07N TO 10N BETWEEN 136W AND 138W.

...DISCUSSION...

ALOFT...A TROUGH/RIDGE PATTERN DOMINATES THE MAJORITY OF THE 
FORECAST AREA. AN UPPER LEVEL TROUGH ENTERS THE REGION NEAR 
30N124W THEN CONTINUES SW TO NEAR 19N136W. SE OF THE TROUGH... 
AN ANTICYCLONE IS CENTERED NEAR 17N115W. THE ASSOCIATED 
ANTICYCLONIC FLOW COVERS THE WATERS TO SE OF THE TROUGH. UPPER 
DIFFLUENCE ON THE SOUTHERN PERIPHERY OF THE RIDGE IS HELPING TO 
INDUCE SOME CONVECTIVE ACTIVITY ALONG THE MONSOON TROUGH/ITCZ AS 
PREVIOUSLY DESCRIBED. THE UPPER TROUGH WILL GRADUALLY DISSIPATE 
ON SUN WITH A RIDGE BUILDING ALONG 125W BY MON. THE RIDGE WILL  
SHIFT EASTWARD TO ALONG 120W BY TUE AS ANOTHER UPPER-LEVEL 
TROUGH REACHES THE FAR NW CORNER OF THE FORECAST AREA. 

AT THE SURFACE...A 1027 MB HIGH PRES IS CENTERED N OF THE 
DISCUSSION AREA NEAR 33N135W WITH A RIDGE EXTENDING SE TO NEAR 
20N120W. HIGH PRES GENERALLY COVERS THE WATERS N OF 15N W OF 
115W. PRES GRADIENT BETWEEN THIS HIGH AND A TROUGH OVER NW 
MEXICO IS SUPPORTING NW-N WINDS OF 20-25 KT N OF 23N BETWEEN 
120W AND 130W WITH SEAS TO 9 FT. THE HIGH IS FORECAST TO REMAIN 
NEALY STATIONARY DURING THE NEXT 48 HOURS WHILE WEAKENING. AS A 
RESULT...THE NW-N 20-25 KT WINDS WILL DIMINISH. HOWEVER... 
ANOTHER SET OF NW SWELL WILL INVADE THE NW WATERS...KEEPING SEAS 
IN THE 8-9 FT RANGE DURING THE NEXT COUPLE OF DAYS. A TIGHT PRES 
GRADIENT TO THE SOUTH OF A HIGH PRES SYSTEM OVER THE GREAT BASIN 
OF UNITED STATES WILL CONTINUE TO BRING FRESH TO STRONG NW WINDS 
ACROSS THE NORTHERN AND CENTRAL SECTIONS OF THE GULF OF 
CALIFORNIA THROUGH THIS AFTERNOON BEFORE DIMINISHING TO 20 KT OR 
LESS THIS EVENING. THE 0420 UTC ASCAT PASS PROVIDED OBSERVATIONS 
OF 20-25 KT NW WINDS ACROSS THE GULF OF CALIFORNIA N OF 26N. 

ON THE SOUTHERN PERIPHERY OF THE SURFACE RIDGE...AN AREA OF 
FRESH TO STRONG TRADE WINDS CAN BE FOUND FROM 10N TO 20N W OF 
130W. SCATTEROMETER DATA CORROBORATED THE PRESENCE OF THESE WIND 
SPEEDS. THIS AREA OF TRADES THEN SHRINKS FROM ABOUT 09N-20N W OF 
135W IN 48 HRS AS THE HIGH WEAKENS AS MENTIONED ABOVE.

SATELLITE IMAGERY AND GLOBAL MODEL GUIDANCE CONTINUE TO SHOW A 
TRIO OF WEAK CIRCULATIONS ALONG THE MONSOON TROUGH AXIS. ON THE 
0600 UTC SURFACE ANALYSIS...THESE WEAK LOWS ARE LOCATED NEAR 
10N96W...11N107W AND 11N121W. THE ONE LOCATED NEAR 11N107W IS 
PRODUCING LIMITED SHOWER AND THUNDERSTORM ACTIVITY. 
DEVELOPMENT...IF ANY...OF THIS SYSTEM IS EXPECTED TO BE SLOW TO 
OCCUR AS IT MOVES WEST-NORTHWESTWARD AT 10 TO 15 MPH. THIS 
SYSTEM HAS CURRENTLY A LOW CHANCE OF BECOMING A TROPICAL CYCLONE 
DURING THE NEXT 48 HOURS. OPERATIONAL AND ENSEMBLE MODELS ARE IN 
GOOD AGREEMENT SHOWING THE EASTERN MOST LOW PRES AREA WEAKENING 
SLIGHTLY AS IT DRIFTS W...BUT DEEPEN THE OTHER TWO SYSTEMS A BIT 
THROUGH 48 HOURS. THE 0556 UTC ASCAT PASS SHOWS NLY WINDS OF 20 
KT WITHIN AROUND 240 NM NW SEMICIRCLE OF LOW PRES CENTERED NEAR 
11N121W AS A RESULT OF THE PRES GRADIENT BETWEEN THIS LOW AND 
HIGH PRES TO THE NW.  

CLIMATOLOGICALLY OCTOBER MARKS THE BEGINNING OF THE TEHUANTEPEC 
WIND EVENTS. PRESENTLY...A COLD FRONT IS MOVING THROUGH THE GULF 
OF MEXICO ACCOMPANIED BY A COOLER AND DRIER AIRMASS. THIS DENSER 
AIR HAS ALREADY SPILLED THROUGH THE CHIVELA PASS INTO THE GULF 
OF TEHUANTEPEC AND IS FORECAST TO REACH 25-30 KT BY EARLY THIS 
MORNING. THIS EVENT IS EXPECTED TO PERSIST THROUGH THE WEEKEND 
WITH WINDS DIMINISHING TO 20-25 KT SUN NIGHT. WAVEWATCH GUIDANCE 
BUILDS SEAS 8-11 FT IN THE GULF.

$$
GR