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Tropical Storm MADELINE Forecast Discussion Number 4
2016-08-27 16:37:50| National Hurricane Center (East Pacific)
Issued at 800 AM PDT SAT AUG 27 2016 000 WTPZ44 KNHC 271437 TCDEP4 TROPICAL STORM MADELINE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142016 800 AM PDT SAT AUG 27 2016 A GPM overpass from 1146 UTC indicated that the low-level center of Madeline was located northeast of previous estimates, near the northeastern edge of the convection. This is consistent with the moderate northeasterly shear analyzed over the cyclone by the SHIPS model output based on the GFS and ECMWF fields. The initial intensity is held at 45 kt for this advisory in agreement with the latest Dvorak estimates from TAFB and SAB, and this value is also close to the latest UW-CIMSS SATCON analysis. Given the relocation of the center, the best estimate of the initial motion is an uncertain 310/08. Madeline is expected to continue moving generally northwestward for the next 72 hours around the southwesterly periphery of a mid-level ridge centered near 125W. After that time, a ridge centered north of the Hawaiian Islands becomes the dominant steering mechanism, and should impart a westward motion through the remainder of the forecast period. While the overall track forecast philosophy has not changed, the more northerly initial position has resulted in a northward shift of the guidance envelope and the NHC forecast by 30 to 50 n mi through the forecast period. The new NHC track is near the middle of the guidance envelope and close to the latest multi-model consensus. The SHIPS model shows the shear decreasing over Madeline during the next 12 hours or so, which should allow for some intensification through 72 hours while the cyclone is moving over SSTs above 27C. The NHC forecast continues to show Madeline reaching hurricane intensity in about 36 hours. At days 4 and 5, the SSTs along the track drop below 27C and the westerly shear increases, which should result in some weakening. The new NHC intensity forecast is a little lower than the previous one after 48 hours due to the more northerly track and is near or a little above the latest intensity consensus. It is too early to determine what impacts Madeline could have on the Hawaiian Islands late in the forecast period. It is important to remind users that the average day 4 and 5 track forecast errors for eastern Pacific tropical cyclones are around 145 and 170 miles, respectively. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 15.2N 138.5W 45 KT 50 MPH 12H 28/0000Z 15.9N 139.4W 50 KT 60 MPH 24H 28/1200Z 16.7N 140.7W 60 KT 70 MPH 36H 29/0000Z 17.7N 142.0W 70 KT 80 MPH 48H 29/1200Z 18.8N 143.6W 70 KT 80 MPH 72H 30/1200Z 20.5N 147.0W 70 KT 80 MPH 96H 31/1200Z 21.0N 151.2W 60 KT 70 MPH 120H 01/1200Z 21.0N 155.5W 50 KT 60 MPH $$ Forecaster Brennan
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