000 WTPZ41 KNHC 171439 TCDEP1 TROPICAL STORM KARINA DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112014 800 AM PDT SUN AUG 17 2014 There has been little change to Karina's convective organization since the previous advisory. A large mass of deep convection with cloud tops to near -80C remains sheared to the west and southwest of the partially exposed low-level circulation center due to moderate easterly vertical wind shear. The intensity was increased slightly to 40 kt based on ASCAT data that arrived after the previous advisory had been issued, which showed reliable 38-39 kt wind vectors to the west of the low-level center. Karina has been moving due west or 270/10 kt over the past 6 hours. There is no significant change to previous forecast track or prognostic reasoning. Karina is expected to gradually make a turn toward the west-southwest over the next 24 hours, and then maintain that motion accompanied by a decrease in forward speed through 72 hours as a large ridge to the north of the Hawaiian Island builds southward to the west of the cyclone. After that, the large disturbance located about 700 nmi east of Karina is expected to develop and become a very large circulation, more than than twice the normal size of a tropical cyclone. That system is forecast to dominate the steering flow across much of the eastern North Pacific, producing a long fetch of low- to mid-level southwesterly flow that is expected to gradually steer Karina back toward the east and northeast on Days 4 and 5. It is possible that Karina could stall on Day 3 when steering currents briefly collapse. The NHC forecast track is similar to the previous advisory track and closely follows the consensus model TVCE. The GFS-based SHIPS intensity guidance shows only 7 kt of easterly 850-200 mb wind shear currently affecting Karina, an analysis that appears to be too weak given the large westward displacement of the deep convection. In contrast, UW-CIMSS shear analyses indicate about 15 kt of easterly mid-level shear is affecting the cyclone, which likely better explains the very asymmetric convective cloud pattern. The overall shear pattern is not forecast to change much for the next 5 days, so little change in strength is expected during that time, especially since Karina will be over or near marginal SSTs of 26-26.5C throughout the forecast period. The official intensity forecast is just an update of the previous advisory, and closely follows the ICON intensity consensus model. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 18.0N 128.2W 40 KT 45 MPH 12H 18/0000Z 17.6N 129.5W 40 KT 45 MPH 24H 18/1200Z 16.9N 131.2W 45 KT 50 MPH 36H 19/0000Z 16.4N 132.4W 45 KT 50 MPH 48H 19/1200Z 16.2N 133.1W 50 KT 60 MPH 72H 20/1200Z 16.2N 133.8W 45 KT 50 MPH 96H 21/1200Z 16.4N 134.1W 45 KT 50 MPH 120H 22/1200Z 16.6N 133.3W 45 KT 50 MPH $$ Forecaster Stewart