000
AXPZ20 KNHC 092154
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC FRI JAN 09 2009

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...

ITCZ AXIS IS CENTERED ALONG 06N77W TO 05N82W TO 04N97W TO 
08N122W TO 06N140W. NUMEROUS MODERATE SCATTERED STRONG 
CONVECTION WITHIN 120 NM N OF AXIS BETWEEN 122W AND 127W. 
SCATTERED MODERATE CONVECTION WITHIN 120 NM N OF AXIS BETWEEN 
138W AND 140W.

...DISCUSSION...

A PAIR OF VIGOROUS SHORTWAVE TROUGHS DIGGING INTO THE CENTRAL 
ROCKIES AND ONTO THE PLAINS SHOULD LEAD TO THE FORMATION OF A 
BROAD LARGE-SCALE TROUGH OVER THE EASTERN CONUS BY THE END OF 
THE WEEKEND. AS THE INITIAL SHORTWAVE IN THE ROCKIES DIVES 
SOUTHEAST TONIGHT...IT SHOULD INTRODUCE A RATHER STRONG COLD 
FRONT THROUGH THE DESERT SOUTHWEST AND EVENTUALLY THROUGH 
NORTHERN MEXICO AND THE NORTHERN GULF OF CALIFORNIA. AFTER THE 
FRONT SWEEPS THROUGH THE REMAINDER OF NORTHWEST MEXICO...THE 
GRADIENT BETWEEN A 1040 MB TO 1043 MB SURFACE RIDGE BUILDING 
BEHIND THE FRONT OVER THE GREAT BASIN AND CENTRAL ROCKIES AND 
LOW PRESSURE TO THE SOUTH SHOULD HERALD THE ARRIVAL OF GALE 
CONDITIONS OVER THE GULF OF CALIFORNIA SAT. THE EVENT IS 
FORECAST TO LAST FOR ALMOST 48 HOURS...WITH THE STRONGEST WINDS 
OF UP TO 45 KT WITH HIGHER GUSTS SLATED FOR SAT. MARINERS CAN 
EXPECT SEAS TO BUILD UP TO 10 OR 11 FT OVER THE NORTH AND UP TO 
8 TO 9 FT IN THE SOUTH IN STEEP NW WIND WAVES.

ELSEWHERE...AFTER A TEMPORARY LULL IN WINDS NEAR AND DOWNSTREAM 
OF THE GULF OF PAPAGAYO...AN ASCAT PASS FROM 1506 UTC CONFIRMS 
THAT GAP WINDS OF 20 TO 25 KT HAVE RETURNED. OVER THE NEXT FEW 
DAYS...STRONG HIGH PRESSURE FORECAST TO BUILD IN THE WAKE OF THE 
LARGE-SCALE TROUGH FORMING OVER THE EASTERN CONUS...WITH THE 
RIDGE BUILDING SOUTHWARD INTO THE CARIBBEAN AND CENTRAL AMERICA. 
AS A RESULT...THE AREAL COVERAGE AND INTENSITY OF GAP WINDS 
DOWNWIND OF THE GULF OF PAPAGAYO SHOULD EXPAND AND INCREASE. IN 
FACT...WITHIN 24 HOURS...MODEL GUIDANCE SUGGESTS THAT NE TO E 
WINDS OF 20 TO 25 KT COULD LIE AS FAR W AS 91W AND WITHIN 60 NM 
EITHER SIDE OF 11N. THE INCREASE IN WIND SHOULD ACTIVATE THE 
OCEAN...AND WAVE HEIGHTS OF UP TO 10 FT ARE EXPECTED IN STEEP 
EASTERLY WIND WAVES. AS THE SURFACE RIDGE OVER THE EASTERN 
STATES WEAKENS A BIT AND SHIFTS E LATER SUN...IT APPEARS AS IF 
GAP WINDS NEAR THE GULF OF PAPAGAYO SHOULD BEGIN TO DECREASE AND 
CONTRACT EASTWARD. HOWEVER...NE WINDS TO 20 KT SHOULD CONTINUE 
VERY NEAR THE COAST PAST THE WEEKEND.

OTHERWISE...THE COLD FRONT ON THE VERGE OF ENTERING NORTHERN 
MEXICO SHOULD PLUNGE SOUTHEAST INTO THE GULF OF MEXICO 
SAT...LEADING TO GALE CONDITIONS IN THE SOUTHWEST GULF LATE SAT 
AND SUN. AS THE STRONG SURFACE HIGH BEHIND THE FRONT BUILDS 
SOUTHWARD INTO NORTHEAST MEXICO AND THE ISTHMUS OF TEHUANTEPEC 
...GAP WINDS IN THE GULF OF TEHUANTEPEC WILL BEGIN TO PICK UP 
LATE SUN AND GALE CONDITIONS ARE EXPECTED IN THE GULF OF 
TEHUANTEPEC EARLY NEXT WEEK.

FINALLY...STRONG SURFACE HIGH PRESSURE BEHIND THE WESTERN CONUS 
SHORTWAVE TODAY SHOULD REST FROM THE INTERMOUNTAIN WEST WESTWARD 
INTO THE MID-LATITUDE NORTHEAST PACIFIC OVER THE WEEKEND. THE 
ENHANCED PRESSURE GRADIENT SOUTH OF THE RIDGE SHOULD ENSURE 
ABOVE NORMAL TRADES BLOWING OVER THE NW PART OF THE FORECAST 
AREA OVER THE NEXT FEW DAYS...A REINFORCEMENT TO THE PATTERN 
WHICH CURRENTLY EXISTS. CONSEQUENTLY...MARINERS CAN EXPECT 8 TO 
10 FT SEAS IN A MIXTURE OF NW SWELL AND ROUGH NE WIND WAVES OVER 
MUCH OF THIS AREA...ESPECIALLY OVER THE AREA FROM 10N TO 20N W 
OF 130W. IN ADDITION...FRESH NORTHERLY SWELL SHOULD ENTER THE 
FAR NORTHERN WATERS BY TONIGHT N OF 27N ROUGHLY BETWEEN 120W AND 
130W AND SPREAD SOUTHWARD.  SEAS OF 8 TO 11 FT OVER THIS AREA 
SHOULD SUBSIDE A BIT BY LATE SAT AND SUN...AS LONGER PERIOD NW 
SWELL BECOMES DOMINANT OVER THE NORTHERN HALF OF THE AREA.

$$
KIMBERLAIN