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Tropical Storm KARINA Forecast Discussion Number 20
2014-08-17 22:44:45| National Hurricane Center (East Pacific)
Issued at 200 PM PDT SUN AUG 17 2014 000 WTPZ41 KNHC 172044 TCDEP1 TROPICAL STORM KARINA DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL EP112014 200 PM PDT SUN AUG 17 2014 Karina's convective pattern has continued to wax and wane over the past 6 hours. Another burst of deep convection with cloud tops to -80C has developed near and to the west through southwest of the partially exposed, well-defined low-level circulation center. Recent objective intensity analyses from CIMSS AMSU and ADT yield estimates of 42-44 kt, and a recent ASCAT-B overpass at 1847 UTC indicated several 36-37 kt surface wind vectors northwest and west of the center. Based on a blend of these values, the initial intensity is held at 40 kt. Karina appears to have made the much expected turn toward the west-southwest, and the initial motion is now 255/11 kt. Karina is expected to continue moving toward the west-southwest and slow down considerably over the next 72 hours as a broad high pressure system builds to the north and west of the cyclone. Karina could even stall on Day 3 as steering currents collapse. After that, a large developing disturbance located about 700 n mi east of the cyclone is forecast by all of the global models to evolve into an unusually large low pressure system that will gradually pull Karina back to the east-northeast and northeast on Days 4 and 5. The official forecast track has been shifted farther west, but not as far west as the consensus model TVCE due to the uncertainly involved in exactly how much influence and timing that the large disturbance east of Karina will have on the tropical cyclone. Moderate easterly mid- to upper-level shear is expected to affect Karina for the next 18 hours or so, which should inhibit any significant intensification. After that, however, the shear is forecast by the SHIPS model to decrease to less than 10 kt, during which time some intensification could occur while the cyclone remains over marginal SSTS of at least 26C. By 48 hours and beyond, the easterly shear is expected to increase again due to strong upper-level outflow associated with the aforementioned large disturbance to the east of Karina. The increasing shear, coupled with decreasing SSTs, should cap any intensification that might have occurred. The GFDL and HWRF models bring Karina back to hurricane strength at around 120 hours, but this seems unlikely due to the cyclone being over sub-26C SSTs at that time. The NHC intensity forecast is similar to the previous advisory and TO the ICON intensity consensus model. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 17.7N 129.5W 40 KT 45 MPH 12H 18/0600Z 17.3N 130.8W 40 KT 45 MPH 24H 18/1800Z 16.7N 132.3W 45 KT 50 MPH 36H 19/0600Z 16.3N 133.4W 45 KT 50 MPH 48H 19/1800Z 16.3N 134.3W 50 KT 60 MPH 72H 20/1800Z 16.4N 135.0W 45 KT 50 MPH 96H 21/1800Z 16.7N 135.2W 45 KT 50 MPH 120H 22/1800Z 17.1N 134.4W 45 KT 50 MPH $$ Forecaster Stewart
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