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Tropical Storm DARBY Forecast Discussion Number 33
2016-07-19 22:33:31| National Hurricane Center (East Pacific)
Issued at 200 PM PDT TUE JUL 19 2016 000 WTPZ45 KNHC 192033 TCDEP5 TROPICAL STORM DARBY DISCUSSION NUMBER 33 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 200 PM PDT TUE JUL 19 2016 Although Darby continues to exhibit a well-defined circulation, deep convection, in the form of ragged bands, continues to gradually diminish in coverage. The initial intensity is subsequently lowered to 55 kt and reflects the Dvorak intensity estimates from both TAFB and SAB. The cyclone is forecast to move over marginal SSTs and into a drier, more stable air mass with increasing modest southwesterly shear during the next several days. The official forecast indicates slight weakening during the next day or so, with very little change in strength through 96 hours as Darby traverses a slightly warmer ocean. Thereafter, Darby is expected to again weaken as it gains latitude and moves into a region of strong southwesterly shear. The official forecast is weighed heavily on the IVCN consensus and lies above the LGEM and Decay SHIPS. It should be noted that longer-range, i.e. day 4 and 5, intensity predictions have little skill. A series of microwave images reveal an apparent northward tilt with height of the cyclone. Consequently, the conventional satellite position estimates have been consistently a little north of the microwave fixes. Using a blend of these fixes, the initial motion is estimated at 280/11 kt. The synoptic reasoning for the track forecast has not changed, as Darby will be steered generally westward during the next 4 days. Through the remaining portion of the forecast, the cyclone is expected to decrease its forward speed and gradually begin to recurve northwestward into a growing weakness caused by an amplifying mid- to upper-level trough north of the Hawaiian Islands. The ECMWF global model has shifted farther south than the previous runs. This shift has also nudged the multi-model consensus south as well, and the official forecast follows suit and is close the GFS and ECMWF ensemble mean guidance. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 19.9N 136.6W 55 KT 65 MPH 12H 20/0600Z 20.0N 138.3W 50 KT 60 MPH 24H 20/1800Z 20.0N 140.6W 45 KT 50 MPH 36H 21/0600Z 19.7N 142.8W 45 KT 50 MPH 48H 21/1800Z 19.4N 145.1W 45 KT 50 MPH 72H 22/1800Z 19.2N 149.3W 45 KT 50 MPH 96H 23/1800Z 19.9N 152.0W 45 KT 50 MPH 120H 24/1800Z 21.6N 153.7W 40 KT 45 MPH $$ Forecaster Roberts
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