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Chill falls over the Atlantic as the official season heads towards close
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| #875622 (Received by flhurricane at: 4:55 PM 22.Sep.2016) TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 34 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 500 PM AST THU SEP 22 2016 Air Force Reserve and NOAA Hurricane Hunter aircraft have been flying in Karl, and the data indicate that the cyclone has re-intensified to a 35-kt tropical storm. The maximum 850-mb flight-level wind so far is 45 kt, which equates to an intensity of about 35 kt. This is also supported by SFMR observations. In addition, dropsonde data suggest lowering the central pressure down to 1005 mb. Combined with the aircraft data, scatterometer winds within the convective bands indicate that tropical-storm-force winds extend 120 nm to the north of the center of circulation. Karl has continued its northwestward progression at 305 degrees with a speed of 14 knots. The synoptic pattern around this system features a mid-level high off to its northeast while a mid-level low is positioned to the north of Puerto Rico. Karl is forecast to move around the western extent of the anticyclone which will make it turn more northward by 36 hours before accelerating northeastward into the mid-latitude westerlies by 48 hours. Based on the adjustment of the initial position provided by the aircraft, the track guidance has shifted a bit left of the positions indicated in the previous advisory. As a result, the updated official forecast has been adjusted westward during the first 48 hours, lying a bit closer to the GFS/GEFS mean clustering while giving some credit to the TVCN multi-model consensus. Later in the period, the ECMWF solution was deemed too slow and was not weighted as heavily at that point. Karl lies right along the edge of a zone of higher shear to its west, and the various analyses are showing about 15 to 20 knots of southeasterly shear over the system. The global models continue to show the shear decreasing at least some during the next couple of days, but there are differences. For example, GFS fields show the shear decreasing to around 5 knots or less by Friday morning through evening, while the ECMWF only shows the shear decreasing to around 10 knots during the same period. This continues to make the intensity forecast difficult. At this point, the intensity forecast was generally left unchanged which allows Karl to become a Category 1 hurricane by Sunday. Based on the latest forecast, the western edge of the tropical-storm-force wind field could begin to affect Bermuda during the next 24 to 36 hours. The Bermuda Weather Service has therefore issued a Tropical Storm Warning for the island. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 25.5N 63.2W 35 KT 40 MPH 12H 23/0600Z 26.8N 64.4W 40 KT 45 MPH 24H 23/1800Z 28.8N 65.1W 45 KT 50 MPH 36H 24/0600Z 30.8N 64.2W 50 KT 60 MPH 48H 24/1800Z 32.7N 61.0W 60 KT 70 MPH 72H 25/1800Z 39.7N 47.0W 70 KT 80 MPH 96H 26/1800Z 49.0N 29.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 27/1800Z...DISSIPATED $$ Forecaster Campbell/Rubin-Oster/Berg |
