000 WTPZ41 KNHC 151452 TCDEP1 TROPICAL STORM KARINA DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112014 800 AM PDT FRI AUG 15 2014 Karina is displaying quite vigorous convection with very cold cloud tops, but almost exclusively in the southwestern semicircle - a classic symptom of moderate vertical shear. The 15-20 kt deep layer shear continues to cause some weakening as the TAFB and SAB Dvorak and CIMSS AMSU estimates suggest an intensity of around 55 kt. The CIMSS ADT, on the other hand, does not recognize the shear pattern in the deep convection and is likely substantially too high. The current intensity is analyzed at 55 kt. The short-term trend in intensity - primarily driven by the hostile vertical shear - suggests some further weakening, which is consistent with all the intensity guidance. The official intensity forecast out through two days is thus slightly below that from the previous advisory. In about 36 hours, the shear should abate some, but the SSTs and atmospheric instability should decrease along the forecast track. The guidance responds by making almost no change to the intensity out through three days. At days four and five, some of the guidance suggests a re-invigoration of Karina. However, because of the rather high uncertainty of Karina's position and possible interaction with other disturbances, the intensity forecast shows no change at the long-lead predictions. The initial motion is now 280/10. Karina remains on the south side of a mid-level ridge that extends from the southwestern United States westward over the Pacific. This feature should steer the storm generally westward for the next couple of days with a slight turn toward the west-southwest by day three. After that time, the guidance becomes divergent, partly due to how the models show Karina interacting with other nearby tropical disturbances. The ECMWF model forecasts a low pressure area east of Karina causing the cyclone to turn farther west-southwestward. The UKMET and NAVGEM also show a low to the east. However, they forecast it to have less influence on Karina, with the UKMET showing a continued westward track and the NAVGEM showing a turn toward the north. The new GFS has changed and now also shows a northward turn at day five. Given the uncertainty, the new forecast track shows a west-southwestward turn at day three followed by a westward shift by day five in best agreement with the variable consensus model. The new forecast track is nearly the same as the previous advisory, except slightly slower to the west at days four and five. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 17.4N 120.2W 55 KT 65 MPH 12H 16/0000Z 17.8N 121.9W 50 KT 60 MPH 24H 16/1200Z 18.1N 124.1W 45 KT 50 MPH 36H 17/0000Z 18.4N 126.2W 45 KT 50 MPH 48H 17/1200Z 18.4N 128.2W 45 KT 50 MPH 72H 18/1200Z 17.7N 131.6W 45 KT 50 MPH 96H 19/1200Z 17.5N 134.5W 45 KT 50 MPH 120H 20/1200Z 17.5N 135.5W 45 KT 50 MPH $$ Forecaster Landsea