000
AXPZ20 KNHC 171534
TWDEP 

TROPICAL WEATHER DISCUSSION    
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC TUE MAR 17 2009

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

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1515 UTC.

...ITCZ...
THE ITCZ AXIS WAS ALONG A LINE FROM 05N77W TO 05N93W TO 03N110W 
TO 08N140W. NO SIGNIFICANT CONVECTION ALONG THE ITCZ.

...DISCUSSION...

THE DEEP LAYER LOW N OF HAWAII IS DRIFTING SE DURING THE PAST 
SEVERAL HOURS AND APPEARS MORE WELL DEFINED IN WATER VAPOR 
IMAGERY. THIS LOW IS FORECAST TO GRADUALLY WEAKEN AND MOVE MORE 
E-NE OVER THE NEXT FEW DAYS...AND ACT TO TEMPORARILY SHIFT THE 
SUBTROPICAL RIDGE OVER N CENTRAL WATERS FARTHER NORTHWARD. THIS 
LOW IS EXPECTED TO PHASE WITH THE NORTHERN STREAM TROUGH 
CURRENTLY APPROACHING IT FROM THE NW...AND MOVE EASTWARD THROUGH 
THE N WATERS. TROUGHING AT LOW LEVELS ASSOCIATED WITH THIS LOW 
WILL WILL MAINTAIN A WEAK FRONTAL BOUNDARY OVER THE NW WATERS 
THROUGH THU. NW SWELL ASSOCIATED WITH A STRONG MID LATITUDE 
SYSTEM FARTHER N HAS BEGUN TO INVADE NW PORTIONS OF THE AREA 
OVERNIGHT...AND WILL BUILD DURING THE NEXT 24 HOURS.

UPPER LEVEL TROUGH IS SLOWLY LIFTING NWD OVER THE NRN GULF OF 
MEXICO AND IS GRADUALLY BEING REPLACED BY A FLAT RIDGE NOW 
LOCATED OVER MEXICO. ASSOCIATED SURFACE COLD FRONT IS MOVING 
EASTWARD THROUGH THE SOUTHWEST GULF OF MEXICO. WEAKENING HIGH 
PRESSURE OVER NRN MEXICO HAS ALLOWED THE PRESSURE GRADIENT TO 
RELAX OFF THE W CENTRAL COAST OF BAJA CALIFORNIA WITH THE LATEST 
QUIKSCAT PASS INDICATING WINDS HAVE DROPPED OFF TO LESS THAN 20 
KT ALONG THE IMMEDIATE COAST OF BAJA CALIFORNIA. 

A BROAD ZONE OF 20-25 KT NE TO E WINDS TO THE SOUTH OF THE 
SUBTROPICAL RIDGE WAS YIELDING A CONVERGENCE LINE AND SCATTERED 
MODERATE CONVECTION WAS INDICATED WITHIN 60 NM EITHER SIDE OF A 
LINE FROM 10N135W TO 12N123W. NORTH OF THIS CONVERGENCE 
ZONE...AND WITHIN THIS BROAD E-NE WIND FETCH...SEAS OF 8 TO 11 
FT PERSIST IN A CONFUSED MIX OF MERGING NW AND SW LONG PERIOD 
SWELL...AND NE WIND WAVES. WAVE HEIGHTS THERE WILL SLOWLY 
SUBSIDE OVER THE NEXT 48 HOURS AS THE SW SWELL FADES AND THE NW 
SWELL BECOMES DOMINANT.

GAP WINDS...
STRONG NORTHERLY FLOE BEHIND THE GULF COLD FRONT HAS PUSHED 
THROUGH THE ISTHMUS OF TEHUANTEPEC WITH A 1218 UTC HIGH 
RESOLUTION QUIKSCAT PASS INDICATING N TO NE WINDS OF 30 TO 35 
KT. THESE WINDS ARE EXPECTED TO DROP BELOW GALE FORCE BY THIS 
EVENING BUT CONTINUE TO BLOW AT 20 TO 30 KT OVER THE NEXT 36 TO 
48 HOURS WITH SOME DIURNAL VARIATIONS IN THE WIND SPEED 
EXPECTED. 
 
WINDS SHOULD CONTINUE TO PULSE UP AND DOWN BUT REMAIN AT OR 
ABOVE 20 KT THROUGH THE FORECAST PERIOD ACROSS AND DOWNWIND A 
SHORT DISTANCE OF THE GULF OF PAPAGAYO...AS STRONG TRADE WINDS 
MOVE THROUGH CENTRAL AMERICA.  THE HIGH PRESSURE RIDGE ACROSS 
THE EASTERN GULF OF MEXICO HAS BEGUN TO SHIFT SOUTHWARD INTO THE 
NW CARIBBEAN AS THE COLD FRONT OVER THE NORTHERN GULF HAS BEEN 
DRAGGED EASTWARD. THIS WILL ALLOW THE PRESSURE GRADIENT TO  
BUILD BETWEEN THIS RIDGE AND THE CLIMATOLOGICAL LOW PRESSURE 
OVER NORTHERN COLOMBIA...AND AID IN ENHANCING GAP FLOW FROM THE 
SOUTHWEST CARIBBEAN ACROSS CENTRAL AMERICA THROUGH THE FORECAST 
PERIOD. THIS IS ALSO EXPECTED TO MAINTAIN A 20 KT FLOW DOWNWIND 
OF THE GULF OF PANAMA...WITH LITTLE CHANGE EXPECTED THERE ALSO 
OVER THE NEXT TWO DAYS.

$$
COBB