000
AXPZ20 KNHC 200956
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC MON DEC 20 2010

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

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0945 UTC.

...TROPICAL LOWS...

.A PERSISTENT SURFACE LOW PRES IS MEANDERING NEAR 07N85W 
ESTIMATED AT 1009 MB. SCATTERED MODERATE CONVECTION IS NOTED 
WITHIN ABOUT 240 NM E OF CENTER. SOUTHWESTERLY WINDS AT 15 TO 20 
KT ARE NOTED WITHIN ABOUT 180 NM OVER THE SE QUADRANT WITH SEAS 
TO 7 FT. THE LOW IS EXPECTED TO MEANDER IN THE SAME AREA THROUGH 
48 HOURS WITH LITTLE CHANGE IN WIND AND SEAS.

.A SURFACE LOW PRES IS CENTERED AT 08N118W AND IS ESTIMATED AT 
1010 MB AND APPEARS TO BE WEAKENING. SOUTHWESTERLY WINDS AT 15 TO
20 KT ARE NOTED WITHIN ABOUT 120 NM OVER THE SE QUADRANT WITH 
SEAS TO 8 FT. OVERALL CONVECTION HAS BEEN DECREASING...BUT 
ISOLATED TO SCATTERED MODERATE CONTINUES TO FLARE WITHIN ABOUT 
240 NM OF THE LOW CENTER.THE LOW IS EXPECTED TO MOVE W NW TO 
NEAR 12N119W 1008 MB IN 24 HOURS. THE LOW IS EXPECTED TO WEAKEN 
TO AN OPEN TROUGH EXTENDING FROM 09N122W TO 18N119W IN 48 HOURS. 
NE TRADES WINDS AT 15 KT ENHANCED W OF THE TROUGH...AND SEAS TO 
8 FT...  WILL EXTEND W TO BEYOND 140W. CROSS EQUATORIAL SE WINDS 
WILL SPREAD N OVER THE PACIFIC WATERS S OF 05N W OF 120W IN 24 
HOURS WITH THE CONDITIONS SPREADING NORTHWARD COVERING THE AREA 
S OF 08N W OF 120W IN 48 HOURS. 

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE AXIS EXTENDS FROM 09N83W TO 
THE LOW PRES CENTERED AT 07N85W...DROPS SW TO NEAR 04N90W THEN 
TURNS NW TO THE LOW PRES AT 08N118W. THE AXIS THEN EXTENDS SW 
TO BEYOND 05N140W. OTHER THAN THE CONVECTION ASSOCIATED WITH THE 
EMBEDDED LOW CENTERS PREVIOUSLY MENTIONED THERE IS NO 
SIGNIFICANT CONVECTION AT THE MOMENT.

...DISCUSSION...

AN UPPER RIDGE EXTENDS NE INTO THE DISCUSSION AREA TO A CREST AT 
25N230W. A SLIGHTLY NEGATIVE TILT UPPER TROUGH IS PASSING 
EASTWARD TO THE N OF THIS RIDGE...WITH ITS MEAN AXIS N OF 27N 
ALONG 135W. THE ASSOCIATED SURFACE FRONT HAS SLOWED ALONG 
30N125W TO 25N140W. TO THE E OF THE UPPER RIDGE AN UPPER TROUGH 
IS DISSECTING THE DISCUSSION AREA FROM 32N112W TO 24N120W TO A 
WEAK UPPER CYCLONE AT 13N130W WITH THE TROUGH CONTINUING S TO 
BASE AT 03N130W. AN UPPER ANTICYCLONE IS CENTERED AT 14N107W 
WITH A RIDGE EXTENDING NE ACROSS OLD MEXICO TO A CREST 
COLLAPSING SE OVER TEXAS AT 32N100W. A 750 NM WIDE DENSE 
MOISTURE PLUME...ORIGINATING IN THE CENTRAL PACIFIC...IS 
STREAMING E WITH SOME OF THE MOISTURE TURNING SE AND S ACROSS 
THE UPPER RIDGE...BUT EVAPORATES ALONG 20N BETWEEN 127W AND 
140W. HOWEVER...MOST OF THE UPPER MOISTURE CONTINUES ESE INTO 
THE NEGATIVE TILT UPPER TROUGH...THEN TURNS NE THROUGH THE 
TROUGH AXIS AND AROUND THE NW PERIPHERY OF THE UPPER RIDGE... 
ROUGHLY OVER THE DISCUSSION AREA N OF POINTS 25N135W AND 
30N108W. SOME OF THIS MOISTURE CONTINUES E ACROSS THE SOUTHERN 
UNITED STATES. SINCE THIS MOISTURE PLUME EXTENDS THOUSANDS OF 
MILES INTO THE CENTRAL PACIFIC AND CONTINUES TO BE REINFORCED 
WITH ADDITIONAL DEBRIS MOISTURE...IT APPEARS THAT IT WILL 
CONTINUE TO BE A PROBLEM FOR THE PRECIPITATION ISSUES OVER THE
SW CONUS.

UPPER DIFFLUENCE OVER THE DEEP TROPICS IN THE VICINITY OF  
10N113W OCCASIONALLY ENHANCES CONVECTION ASSOCIATED WITH THE 
SURFACE CYCLONE AT 08N118W. DEBRIS MOISTURE FROM PREVIOUS 
CONVECTION HAS FANNED OVER THE AREA FROM 07N TO 14N BETWEEN 110W 
AND 117W. 

A UPPER RIDGE EXTENDS W ACROSS COLOMBIA TO CREST OVER THE 
PACIFIC AT 08N79W. AN UPPER TROUGH EXTENDS SW ACROSS THE NW 
CARIBBEAN AND OVER CENTRAL AMERICA INTO THE PACIFIC ALONG 11N82W 
TO 01N85W. A SECOND UPPER TROUGH IS NOTED ALONG 16N88W TO 
04N102W. AN UPPER ANTICYCLONE IS NOTED BETWEEN THESE UPPER 
TROUGHS...NEAR 10N88W. ISOLATED CONVECTION FLARED EARLIER OVER 
PANAMA AND COSTA RICA WITH THE DEBRIS MOISTURE EVAPORATING OVER 
THE PACIFIC N OF THE EQUATOR TO THE E OF 87W.  OTHERWISE THE 
UPPER LEVELS ARE VERY DRY S OF 20 W OF 125W AND S OF 27N E OF 
125W...AND IS SUPPRESSING CONVECTION.
    
THE SURFACE COLD FRONT THAT EXTENDS FROM 32N125W TO 25N140W IS 
ACCOMPANIED BY A 20 KT WIND SHIFT ALONG THE FRONT WITH SEAS 
BUILDING TO 14 FT W OF THE FRONT PRIMARILY IN LONG PERIOD NW 
SWELL. THIS INITIAL FRONT WILL CONTINUE TO SLOW AND WEAKEN TILL 
A SECOND COLD FRONT...MOVING INTO THE NW PORTION TONIGHT... 
OVERTAKES THE INITIAL FRONT WED REACHING THE NORTHERN BAJA 
CALIFORNIA PENINSULA LATE WED. SEAS W OF THE FRONT WILL BUILD
TO ABOUT 16 FT IN LONG PERIOD NW SWELL...BUT ARE EXPECTED TO 
SUBSIDE TO ABOUT 10 FT BEFORE REACHING THE NORTHERN BAJA 
CALIFORNIA PENINSULA.    
  
GAP WINDS...ALTHOUGH SOUTHERLY RETURN IS WELL ESTABLISHED OVER 
THE GULF OF MEXICO...EXPECT SOME LATE NIGHT DRAINAGE FLOW TO 
RESULT IN NORTHERLY 15 TO 20 KT WINDS IN THE GULF OF TEHUANTEPEC 
AROUND SUNRISE THIS MORNING AND TUE MORNING...AND INCREASE TO 20 
TO 25 KT WED MORNING...AND PERHAPS 25 TO 30 KT THU MORNING. 
DEPENDING ON THE STRENGTH OF THE PERSISTENT LOW PRESSURE NEAR 
07N85W...EXPECT NE WINDS TO CONTINUE PULSE AT 15 TO 20 KT IN THE 
GULF OF PAPAGAYO...AND PERHAPS A LITTLE STRONGER ON TUE.

GULF OF CALIFORNIA...AS THE COLD FRONT APPROACHES THE NORTHERN 
BAJA CALIFORNIA PENINSULA WED...SOUTHERLY WINDS WILL INCREASE 
FROM 15 KT TO 20 TO 25 KT OVER THE GULF CALIFORNIA N OF 30N WED 
AFTERNOON.
        
$$
NELSON