000 WTPZ42 KNHC 220834 TCDEP2 TROPICAL STORM ANDRES DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP022009 200 AM PDT MON JUN 22 2009 ENHANCED INFRARED SATELLITE IMAGES SHOW VERY COLD CLOUD TOPS...WITH SOME BANDING FEATURES OVER THE SOUTHERN AND WESTERN SEMICIRCLES OF THE TROPICAL STORM. CURRENT INTENSITY IS SET AT 45 KT IN ACCORDANCE WITH THE LATEST DVORAK ESTIMATE FROM TAFB. THIS IS ALSO IN AGREEMENT WITH A QUIKSCAT PASS FROM SEVERAL HOURS AGO WHICH SHOWED AT LEAST ONE BELIEVABLE WIND VECTOR IN THE 40 TO 45 KT RANGE. ANDRES IS EXPECTED TO REMAIN OVER VERY WARM WATER FOR AT LEAST THE NEXT 36 HOURS...HOWEVER THE SHIPS MODEL PROJECTS 20 TO 25 KT OF EAST-NORTHEASTERLY SHEAR TO AFFECT THE TROPICAL CYCLONE WITHIN THE NEXT DAY OR SO. IT SHOULD BE NOTED THAT THE SHIPS OUTPUT SHOWS THAT THIS DIRECTION OF THE VERTICAL SHEAR VECTOR IS LESS UNFAVORABLE THAN SHEAR FROM SOME OTHER DIRECTIONS. GIVEN THIS AND OTHER FAVORABLE ENVIRONMENTAL FACTORS SUCH AS ABUNDANT LOW- TO MID-LEVEL MOISTURE AND AN ENVIRONMENT OF LOW-LEVEL CYCLONIC VORTICITY...BOTH THE SHIPS AND LGEM PREDICT THAT ANDRES WILL BECOME A HURRICANE IN 24 TO 36 HOURS. THE OFFICIAL FORECAST FOLLOWS SUIT. LATER IN THE FORECAST PERIOD...INCREASINGLY LESS CONDUCIVE ATMOSPHERIC AND OCEANIC CONDITIONS SHOULD INDUCE WEAKENING. INITIAL MOTION IS A SOMEWHAT UNCERTAIN 300/3 AS THE CENTER IS DIFFICULT TO TRACK USING NIGHTTIME SATELLITE IMAGES. THE TRACK FORECAST CONTINUES TO PRESENT A CHALLENGE. MUCH OF THE DYNAMICAL MODEL GUIDANCE SHOW ANDRES MOVING NEAR OR OVER THE SOUTHWEST COAST OF MEXICO. THIS MOTION WOULD APPARENTLY BE THE RESULT OF ANDRES ROTATING AROUND THE EASTERN SIDE OF A BROAD LOW-LEVEL CYCLONIC GYRE WITHIN WHICH IT IS EMBEDDED. HOWEVER THE DYNAMICAL MODEL FORECASTS ALSO SHOW PRONOUNCED MID- TO UPPER- TROPOSPHERIC RIDGING OVER MEXICO...WHICH WOULD TEND TO DRIVE THE TROPICAL CYCLONE ON A MORE WESTWARD TRACK...OR AT LEAST PARALLEL TO THE COAST. THE OFFICIAL FORECAST IS NUDGED A LITTLE TO THE RIGHT OF THE PREVIOUS ONE BUT STILL LIES TO THE LEFT OF THE MODEL CONSENSUS. IN 4 TO 5 DAYS IT IS LIKELY THAT ANDRES WILL BE A WEAKENING SYSTEM BEING STEERED MAINLY BY THE LOWER-LEVEL FLOW. ALTHOUGH THE OFFICIAL FORECAST TRACK STILL DOES NOT EXPLICITLY INDICATE LANDFALL...IT IS NONETHELESS CLOSE ENOUGH TO THE COAST SO THAT A TROPICAL STORM WARNING MAY BE REQUIRED FOR A PORTION OF THE SOUTHWEST COAST OF MEXICO LATER TODAY. FORECAST POSITIONS AND MAX WINDS INITIAL 22/0900Z 15.0N 102.1W 45 KT 12HR VT 22/1800Z 15.6N 102.6W 55 KT 24HR VT 23/0600Z 16.5N 103.3W 60 KT 36HR VT 23/1800Z 17.6N 104.1W 65 KT 48HR VT 24/0600Z 19.0N 105.6W 65 KT 72HR VT 25/0600Z 21.0N 108.5W 55 KT 96HR VT 26/0600Z 21.5N 112.5W 40 KT 120HR VT 27/0600Z 21.5N 117.0W 25 KT $$ FORECASTER PASCH