000
AXPZ20 KNHC 202147
TWDEP 

TROPICAL WEATHER DISCUSSION  
NWS NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC THU JAN 20 2011

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2100 UTC.

...ITCZ...
THE INTERTROPICAL CONVERGENCE ZONE AXIS IS ALONG 06N77W TO 
05N100W TO 06N120W TO 07N130W TO 07N140W. SCATTERED MODERATE 
FROM 03N TO 05N BETWEEN 79W AND 82W...AND WITHIN 100 NM S OF 
AXIS FROM 86W TO 88W. 

...DISCUSSION...
ALOFT...AN UPPER LEVEL TROUGH EXTENDS FROM THE SOUTHWESTERN U.S. 
THROUGH CENTRAL BAJA CALIFORNIA TO 25N130W THEN NW TO 30N140W. 
THIS TROUGH WILL SHIFT E OF THE AREA TONIGHT AND FRI. MODERATE 
TO STRONG MID TO UPPER LEVEL SUBSIDENCE AND IMPLIED DRY AIR MASS 
IS NOTED N OF THE TROUGH AND S OF THE TROUGH TO 22N. AN 70-110 
KT JET STREAM BRANCH EXTENDS FROM THE SOUTHERN TIP OF THE BAJA 
PENINSULA ACROSS NORTHERN MEXICO. A MID/UPPER LEVEL RIDGE 
DOMINATES THE EASTERN PART OF THE FORECAST WATERS PARTICULARLY E 
OF 100W. A DIFFLUENT PATTERN ALOFT ASSOCIATED WITH THIS FEATURE 
IS HELPING TO INDUCE CONVECTION ALONG THE ITCZ E OF 88W. 

AT THE SURFACE...A 1033 MB HIGH PRES CENTERED NEAR 39N135W 
EXTENDS A RIDGE SE OVER THE FORECAST WATERS TO NEAR 20N110W. THE 
PRES GRADIENT BETWEEN THIS HIGH AND LOWER PRESSURE ASSOCIATED 
WITH THE ITCZ SUPPORTS FRESH TRADE WINDS TO 20 KT FROM 10N TO 
20N W OF 130W. AN EARLIER WINDSAT PASS PROVIDED OBSERVATIONS OF 
THESE WIND SPEEDS. THE SURFACE HIGH PRESSURE IS FORECAST TO MOVE 
SW OVER THE NEXT 24 HOURS WHICH WILL MAINTAIN THIS AREA OF FRESH 
TRADES. THE PRESSURE GRADIENT BETWEEN THE SURFACE HIGH MENTIONED 
ABOVE AND THE CALIFORNIA COASTAL TROUGH IS SUPPORTING FRESH TO 
STRONG N TO NE WINDS N OF 20N W OF 125W. THESE WINDS ARE 
FORECAST TO DIMINISH TO 20 KT THROUGH 24 HOURS...THEN TO BELOW 
20 KT WITHIN 48 HOURS AS THE GRADIENT SLACKENS. 

A PAIR OF WEAK TROUGHS ARE WITHIN THE ITCZ. THE EASTERNMOST IS 
ALONG 88W FROM 03N TO 10N. SCATTERED MODERATE CONVECTION IS 
NOTED S OF THE ITCZ AND WITHIN AROUND 100 NM E OF TROUGH. THE 
SECOND TROUGH EXTENDS FROM 14N135W TO 05N135W. ISOLATED MODERATE 
CONVECTION IS NEAR THE INTERSECTION OF THE TROUGH AXIS AND THE 
ITCZ.

LONG PERIOD NW SWELLS WITH PERIODS OF 16-18 SEC ARE REACHING 
100W. A SECOND SET OF LONG PERIOD NW SWELLS WITH SIGNIFICANT 
WAVE HEIGHTS AS HIGH OF 15 FT HAS MOVED INTO THE NW WATERS AND 
WILL CONTINUE TO SPREAD SE ACROSS THE REGIONAL WATERS BY FRI. 
THESE SWELLS...GENERATED FROM A SERIES OF INTENSE LOW PRES 
SYSTEMS WELL NW OF THE REGION...WILL CONTINUE THROUGH 48 HOURS. 

GAP WINDS...
THE NEXT GULF OF TEHUANTEPEC EVENT IS FORECAST TO BEGIN ON FRI 
AS HIGH PRES BUILDS S ACROSS MEXICO AND THE WESTERN GULF OF 
MEXICO IN THE WAKE OF A COLD FRONT THAT MOVES THROUGH THE BAY OF 
CAMPECHE AND SOUTHEASTERN MEXICO. THIS WILL BE A BRIEF EVENT. 

WINDS HAVE ALREADY INCREASED TO 25 KT OVER THE FAR NORTHERN 
PORTION OF THE GULF OF CALIFORNIA. THIS WEATHER PATTERN WILL 
PERSIST OVER THE NEXT 24 HOUR EXTENDING FURTHER S TO 27N AS 
STRONG HIGH PRES BUILDS OVER THE GREAT BASIN REGION.  

$$
GR