000 WTPZ44 KNHC 181430 TCDEP4 TROPICAL DEPRESSION FOUR-E DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042011 800 AM PDT MON JUL 18 2011 SATELLITE IMAGERY INDICATES THUNDERSTORM ACTIVITY HAS BECOME SUFFICIENTLY ORGANIZED NEAR THE CENTER OF THE WELL-DEFINED LOW PRESSURE AREA LOCATED TO THE SOUTH OF GUATEMALA FOR THIS SYSTEM TO BE DESIGNATED AS THE FOURTH TROPICAL DEPRESSION OF THE SEASON. ALTHOUGH SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE ONLY T1.5/25 KT...NHC ADT ESTIMATES INDICATE THE SYSTEM IS NEAR TROPICAL STORM STRENGTH. IN ADDITION...SHIP WDE5381 LOCATED ABOUT 70 NMI NORTH OF THE CENTER REPORTED AN EAST WIND OF 31 KT AT 06Z. THEREFORE...THE INITIAL INTENSITY IS SET AT A CONSERVATIVE 30 KT. THE INITIAL MOTION ESTIMATE IS 280/11. AN EXTENSIVE SUBTROPICAL RIDGE LOCATED ACROSS MOST OF THE UNITED STATES AND EXTENDING SOUTHWARD ACROSS THE GULF OF MEXICO AND INTO MAINLAND MEXICO IS EXPECTED TO KEEP THE SYSTEM MOVING IN A GENERAL WEST-NORTHWESTWARD DIRECTION THROUGHOUT THE FORECAST PERIOD. THE GFDL AND HWRF MODELS ARE FORECASTING THE WESTERN PORTION OF THE RIDGE TO ERODE AFTER 72 HOURS...WHICH WOULD ALLOW THE CYCLONE TO TURN NORTHWESTWARD TOWARD BAJA CALIFORNIA. HOWEVER...THESE APPEAR TO BE OUTLIER SOLUTIONS GIVEN THE CURRENT STRENGTH OF THIS BROAD HEAT-WAVE DOME OF HIGH PRESSURE. AS A RESULT...THE OFFICIAL FORECAST TRACK IS WELL SOUTH OF THE GFDL/HWRF TRACKS AFTER AT 96 AND 120 HOURS...AND IS SIMILAR TO BUT SLIGHTLY SOUTH OF THE GLOBAL MODEL CONSENSUS THROUGHOUT THE FORECAST PERIOD. SATELLITE IMAGERY INDICATES A WELL-DEFINED CURVED BAND OF CONVECTION THAT IS INDICATIVE OF A DEVELOPING TROPICAL STORM. MICROWAVE AND VISIBLE SATELLITE IMAGERY...PLUS THE AFOREMENTIONED SHIP REPORT...ALSO SUGGEST THAT THE DEPRESSION HAS A FAIRLY TIGHT INNER CORE WIND FIELD. ALL OF THIS WOULD INDICATE THAT RAPID INTENSIFICATION IS A DISTINCT POSSIBILITY. HOWEVER...AN INHIBITING FACTOR FOR THE NEXT 24 HOURS IS MODERATE NORTHERLY SHEAR...SO ONLY STEADY STRENGTHENING IS FORECAST. BY 36 HOURS...THE SHEAR IS EXPECTED TO DECREASE TO NEAR 5 KT...WHICH SHOULD ALLOW FOR SIGNIFICANT INTENSIFICATION OF THE CYCLONE. THE OFFICIAL INTENSITY FORECAST IS WELL ABOVE ALL OF THE STATISTICAL INTENSITY GUIDANCE AND CLOSELY FOLLOWS THE GFDL AND HWRF MODELS THROUGH 96 HOURS. AFTER THAT...RAPID WEAKENING IS FORECAST AS THE CYCLONE IS EXPECTED TO MOVE OVER THE COLD WATER TROPICAL CYCLONE GRAVEYARD SITUATED WEST OF 110W LONGITUDE. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 10.6N 91.5W 30 KT 35 MPH 12H 19/0000Z 10.7N 93.1W 40 KT 45 MPH 24H 19/1200Z 11.3N 95.5W 55 KT 65 MPH 36H 20/0000Z 12.3N 98.7W 70 KT 80 MPH 48H 20/1200Z 13.6N 101.5W 85 KT 100 MPH 72H 21/1200Z 16.6N 106.5W 105 KT 120 MPH 96H 22/1200Z 18.8N 110.3W 100 KT 115 MPH 120H 23/1200Z 20.0N 113.0W 70 KT 80 MPH $$ FORECASTER STEWART 000 WTPZ44 KNHC 181430 TCDEP4 TROPICAL DEPRESSION FOUR-E DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042011 800 AM PDT MON JUL 18 2011 SATELLITE IMAGERY INDICATES THUNDERSTORM ACTIVITY HAS BECOME SUFFICIENTLY ORGANIZED NEAR THE CENTER OF THE WELL-DEFINED LOW PRESSURE AREA LOCATED TO THE SOUTH OF GUATEMALA FOR THIS SYSTEM TO BE DESIGNATED AS THE FOURTH TROPICAL DEPRESSION OF THE SEASON. ALTHOUGH SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE ONLY T1.5/25 KT...NHC ADT ESTIMATES INDICATE THE SYSTEM IS NEAR TROPICAL STORM STRENGTH. IN ADDITION...SHIP WDE5381 LOCATED ABOUT 70 NMI NORTH OF THE CENTER REPORTED AN EAST WIND OF 31 KT AT 06Z. THEREFORE...THE INITIAL INTENSITY IS SET AT A CONSERVATIVE 30 KT. THE INITIAL MOTION ESTIMATE IS 280/11. AN EXTENSIVE SUBTROPICAL RIDGE LOCATED ACROSS MOST OF THE UNITED STATES AND EXTENDING SOUTHWARD ACROSS THE GULF OF MEXICO AND INTO MAINLAND MEXICO IS EXPECTED TO KEEP THE SYSTEM MOVING IN A GENERAL WEST-NORTHWESTWARD DIRECTION THROUGHOUT THE FORECAST PERIOD. THE GFDL AND HWRF MODELS ARE FORECASTING THE WESTERN PORTION OF THE RIDGE TO ERODE AFTER 72 HOURS...WHICH WOULD ALLOW THE CYCLONE TO TURN NORTHWESTWARD TOWARD BAJA CALIFORNIA. HOWEVER...THESE APPEAR TO BE OUTLIER SOLUTIONS GIVEN THE CURRENT STRENGTH OF THIS BROAD HEAT-WAVE DOME OF HIGH PRESSURE. AS A RESULT...THE OFFICIAL FORECAST TRACK IS WELL SOUTH OF THE GFDL/HWRF TRACKS AFTER AT 96 AND 120 HOURS...AND IS SIMILAR TO BUT SLIGHTLY SOUTH OF THE GLOBAL MODEL CONSENSUS THROUGHOUT THE FORECAST PERIOD. SATELLITE IMAGERY INDICATES A WELL-DEFINED CURVED BAND OF CONVECTION THAT IS INDICATIVE OF A DEVELOPING TROPICAL STORM. MICROWAVE AND VISIBLE SATELLITE IMAGERY...PLUS THE AFOREMENTIONED SHIP REPORT...ALSO SUGGEST THAT THE DEPRESSION HAS A FAIRLY TIGHT INNER CORE WIND FIELD. ALL OF THIS WOULD INDICATE THAT RAPID INTENSIFICATION IS A DISTINCT POSSIBILITY. HOWEVER...AN INHIBITING FACTOR FOR THE NEXT 24 HOURS IS MODERATE NORTHERLY SHEAR...SO ONLY STEADY STRENGTHENING IS FORECAST. BY 36 HOURS...THE SHEAR IS EXPECTED TO DECREASE TO NEAR 5 KT...WHICH SHOULD ALLOW FOR SIGNIFICANT INTENSIFICATION OF THE CYCLONE. THE OFFICIAL INTENSITY FORECAST IS WELL ABOVE ALL OF THE STATISTICAL INTENSITY GUIDANCE AND CLOSELY FOLLOWS THE GFDL AND HWRF MODELS THROUGH 96 HOURS. AFTER THAT...RAPID WEAKENING IS FORECAST AS THE CYCLONE IS EXPECTED TO MOVE OVER THE COLD WATER TROPICAL CYCLONE GRAVEYARD SITUATED WEST OF 110W LONGITUDE. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 10.6N 91.5W 30 KT 35 MPH 12H 19/0000Z 10.7N 93.1W 40 KT 45 MPH 24H 19/1200Z 11.3N 95.5W 55 KT 65 MPH 36H 20/0000Z 12.3N 98.7W 70 KT 80 MPH 48H 20/1200Z 13.6N 101.5W 85 KT 100 MPH 72H 21/1200Z 16.6N 106.5W 105 KT 120 MPH 96H 22/1200Z 18.8N 110.3W 100 KT 115 MPH 120H 23/1200Z 20.0N 113.0W 70 KT 80 MPH $$ FORECASTER STEWART