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Tropical Depression FOUR-E Forecast Discussion Number 1
2013-06-30 04:38:21| National Hurricane Center (East Pacific)
Issued at 800 PM PDT SAT JUN 29 2013 000 WTPZ44 KNHC 300238 TCDEP4 TROPICAL DEPRESSION FOUR-E DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 800 PM PDT SAT JUN 29 2013 THE AREA OF LOW PRESSURE SOUTHWEST OF ACAPULCO HAS NOW ACQUIRED ENOUGH ORGANIZED DEEP CONVECTION TO BE CONSIDERED A TROPICAL CYCLONE. THE CONVECTIVE PATTERN FEATURES A SMALL AREA OF CENTRAL CONVECTION NEAR AND NORTH OF THE CENTER WITH SOME RAGGED CONVECTIVE BANDS TO THE NORTH AND SOUTHEAST. RECENT MICROWAVE IMAGES SUGGEST THAT THE CENTER MAY BE SOMEWHAT ELONGATED...BUT IT APPEARS TO BE SITUATED NEAR OR JUST TO THE SOUTH OF THE COLDEST CLOUD TOPS. THE INITIAL INTENSITY IS 30 KT BASED ON THE LATEST DVORAK ESTIMATES FROM TAFB AND SAB. THE INITIAL MOTION ESTIMATE IS A SOMEWHAT UNCERTAIN 360/09...GIVEN THAT THE CYCLONE IS STILL IN THE FORMATIVE STAGES. THE SYNOPTIC SITUATION FEATURES A MID/UPPER-LEVEL RIDGE TO THE EAST OF THE DEPRESSION AND AN UPPER-LEVEL LOW TO THE NORTHWEST. THESE FEATURES SHOULD STEER THE CYCLONE GENERALLY NORTHWARD FOR THE NEXT 12 HOURS. THEN THE DEEP-LAYER RIDGE OVER THE WESTERN UNITED STATES IS EXPECTED TO BECOME THE DOMINANT STEERING MECHANISM...WHICH SHOULD RESULT IN THE CYCLONE TURNING TOWARD THE NORTHWEST BY 48 HOURS...FOLLLOWED BY A GRADUAL TURN TOWARD THE WEST BY THE END OF THE PERIOD. THE NHC TRACK FORECAST IS CLOSEST TO THE GFS MODEL TRACK THROUGH THE PERIOD. WHILE THE GLOBAL MODELS ARE IN GOOD AGREEMENT OF THE EVOLUTION OF THE SYNOPTIC PATTERN...SEVERAL OF THEM DO NOT INITIALIZE THE DEPRESSION VERY WELL. GIVEN THIS...CONFIDENCE IN THE DETAILS OF THE TRACK FORECAST IS LOWER THAN AVERAGE. THE ENVIRONMENT APPEARS FAVORABLE FOR STEADY STRENGTHENING DURING THE FIRST 72 HOURS OR SO...AS THE CYCLONE WILL BE OVER VERY WARM WATERS AND IN A LOW SHEAR ENVIRONMENT. HOWEVER...MOST OF THE GUIDANCE SHOWS ONLY MODEST STRENGTHENING. GIVEN THE APPARENTLY FAVORABLE ENVIRONMENT...THE NHC FORECAST IS NEAR THE HIGH END OF THE GUIDANCE AND SHOWS THE CYCLONE NEAR HURRICANE STRENGTH BY 72 HOURS...IN BEST AGREEMENT WITH THE SHIPS AND HWRF MODELS. BY DAY 4...THE CYCLONE WILL BE MOVING OVER COOLER WATERS...WHICH SHOULD RESULT IN SLOW WEAKENING. AFTER COORDINATION WITH THE GOVERNMENT OF MEXICO...A TROPICAL STORM WATCH AND WARNING HAVE BEEN ISSUED FOR A PORTION OF THE SOUTHWEST COAST OF MEXICO. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 13.7N 103.0W 30 KT 35 MPH 12H 30/1200Z 14.9N 103.1W 40 KT 45 MPH 24H 01/0000Z 16.1N 103.7W 45 KT 50 MPH 36H 01/1200Z 17.1N 104.5W 50 KT 60 MPH 48H 02/0000Z 17.9N 105.3W 55 KT 65 MPH 72H 03/0000Z 19.2N 107.0W 60 KT 70 MPH 96H 04/0000Z 19.5N 108.5W 55 KT 65 MPH 120H 05/0000Z 19.5N 111.0W 45 KT 50 MPH $$ FORECASTER BRENNAN
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