000
AXPZ20 KNHC 202148
TWDEP 

TROPICAL WEATHER DISCUSSION     
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC FRI MAR 20 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 
2030 UTC.

...ITCZ...
THE ITCZ AXIS LIES ALONG A LINE FROM 08N83W TO 03N95W TO 02N110W 
02N121W TO 04N131W TO 04N140W. SCATTERED MODERATE CONVECTION IS 
FROM 04N TO 07N BETWEEN 83W AND 86W.

...DISCUSSION...

THE UPPER LEVEL FLOW CONTINUES TO AMPLIFY N OF THE DISCUSSION 
AREA AS AN UPPER LEVEL JET MAXIMUM DIVES SOUTHEASTWARD...FORCING 
AN UPPER TROUGH TO DIG SOUTHWARD TOWARD THE DISCUSSION AREA. AN 
ASSOCIATED COLD FRONT N OF THE AREA CONTINUES ADVANCING 
SOUTHWARD...AND IS FORECAST TO ENTER THE NORTHERN WATERS BY 
SUNDAY. N WINDS OF 20 TO 30 KT WILL AFFECT AREAS IN THE WAKE OF 
THE FRONT...WHERE WAVE HEIGHTS OVER 14 FT IN NORTHWESTERLY SWELL 
WILL BE PRESENT. GALES ARE EXPECTED TO REMAIN N OF THE 
AREA...WHERE THE STRONGER SURFACE PRESSURE GRADIENT WILL BE 
LOCATED.

IN THE MEANTIME...A WEAK SURFACE RIDGE N OF THE DISCUSSION AREA 
CONTINUES TO DISSIPATE IN RESPONSE TO DECREASING DEEP LAYER 
SUBSIDENCE WITH THE AMPLIFICATION OF THE UPPER TROUGH. WAVE 
HEIGHTS UP TO 9 FT IN NORTHWESTERLY SWELL CONTINUE IN NORTH 
CENTRAL PORTIONS OF THE DISCUSSION AREA...BUT CONTINUE SUBSIDING 
AS THEY DEPART THEIR SOURCE REGION AND WINDS DIMINISH. THE 
ENHANCED SURFACE PRESSURE GRADIENT AT THE SOUTHERN PERIPHERY OF 
THE SURFACE HIGH ALSO IS ENHANCING NE TO E TRADE WINDS ACROSS 
THE REGION. THE QUIKSCAT PASS AROUND 20/1420 UTC SHOWED NE TO E 
WINDS UP TO 20 KT FROM 11N TO 17N W OF 130W...WITH WAVEWATCH 
GUIDANCE INDICATING SEAS TO 9 FT IN THIS AREA WITH NW SWELL. THE 
TRADES IN THIS AREA ARE EXPECTED TO PICK UP SUBSTANTIALLY ON 
SUNDAY AS A SURFACE HIGH BUILDS SOUTHWARD IN THE WAKE OF THE 
AFOREMENTIONED COLD FRONT. ALSO...SOUTHWESTERLY SWELL OF UP TO  
8 FT S OF THE AREA WILL MOVE NORTHWARD INTO THE AREA AND MERGE 
WITH NORTHWESTERLY SWELL ACROSS SOUTHERN PORTIONS OF THE AREA BY 
SUNDAY.

AS FOR CONVECTIVE ACTIVITY...UPPER LEVEL DIFFLUENCE N OF THE 
ITCZ AXIS IS SUPPORTING SCATTERED MODERATE CONVECTION FROM 17N 
TO 19N BETWEEN 122W AND 124W. FARTHER TO THE E...DEEP LAYER DRY 
AIR AND STABLE ATMOSPHERIC CONDITIONS EMBEDDED WITHIN AN UPPER 
RIDGE ARE RESULTING IN FAIR WEATHER CONDITIONS S OF 16N E OF 99W.

GAP WINDS...
A PERSISTENT RIDGE OF SURFACE HIGH PRESSURE OVER MEXICO AND THE 
GULF OF MEXICO WILL SUPPORT A RELATIVELY STRONG SURFACE PRESSURE 
GRADIENT ACROSS THE ISTHMUS OF TEHUANTEPEC DURING THE NEXT FEW 
DAYS. CORRESPONDINGLY...THE ASCAT PASS AROUND 20/1620 UTC 
DEPICTED N TO NE WINDS OF 20 TO 25 KT FUNNELING INTO THE GULF OF 
TEHUANTEPEC. STRONG SURFACE HIGH PRESSURE BUILDING SOUTHEASTWARD 
TOWARD THE MID-ATLANTIC STATES OF THE CONUS WILL STEEPEN THE 
PRESSURE GRADIENT ACROSS THE ISTHMUS OF TEHUANTEPEC EVEN FURTHER 
DURING THE NEXT DAY. CORRESPONDINGLY...WINDS WILL INCREASE 
ACROSS A LARGER AREA IN THE GULF OF TEHUANTEPEC. COMPUTER MODEL 
GUIDANCE CONTINUES TO INDICATE THE LIKELIHOOD OF GALE FORCE 
WINDS FROM LATE TONIGHT THROUGH SATURDAY IN THE GULF OF 
TEHUANTEPEC...GIVEN THE STRONG PRESSURE GRADIENT SW OF THE 
SURFACE HIGH. SEAS WILL BUILD OVER 11 FT DOWNWIND OF THE GULF OF 
TEHUANTEPEC BY SATURDAY. ALSO...TRADE WINDS ACROSS THE CARIBBEAN 
CONTINUE WITH A PERSISTENT SURFACE LOW OVER NW COLOMBIA. THESE 
WINDS CONTINUE TO BLEED INTO THE GULF OF PAPAGAYO. GAP WINDS 
AROUND THE GULFS OF TEHUANTEPEC AND PAPAGAYO ARE FORECAST TO BE 
STRONGEST LATE AT NIGHT WHEN DRAINAGE FLOW OFF HIGHER TERRAIN IS 
MAXIMIZED IN THE PRESENCE OF DEEP LAYER DRY AIR.

$$

COHEN