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Tropical Storm MADELINE Forecast Discussion Number 5
2016-08-27 22:33:58| National Hurricane Center (East Pacific)
Issued at 200 PM PDT SAT AUG 27 2016 000 WTPZ44 KNHC 272033 TCDEP4 TROPICAL STORM MADELINE DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142016 200 PM PDT SAT AUG 27 2016 GOES-West visible imagery shows that the center of Madeline is located on the northeastern edge of a ragged area of central convection, with a large convective band wrapping around the western semicircle of the circulation. The initial intensity estimate is 50 kt, which is a blend of the latest subjective and objective Dvorak classifications. The SHIPS model output shows the vertical shear decreasing below 10 kt by tonight, while Madeline is moving over SSTs above 27C. This environment should allow for some additional strengthening during the next 24 to 36 hours. After that time, the tropical cyclone will be moving over cooler SSTs and into a drier environment, with mid-level relative humidity values falling below 50 percent. This should result in gradual weakening, followed by steadier weakening later in the period as the vertical wind shear increases above 20 kt. The new NHC intensity forecast is a little higher than the previous one in the short range given the observed strengthening, and is similar afterward. This forecast is close to or a bit below the latest IVCN consensus. The initial motion estimate is 305/09. The track forecast reasoning remains unchanged, as Madeline should continue moving generally northwestward for the next 48 hours under the influence of mid-level ridge centered well to its northeast. Later in the period, a strengthening mid-level ridge north of the Hawaiian Island will become the dominant steering mechanism and result in a westward or slightly south of due westward track. Through 72 hours the new NHC forecast is largely and update of the previous near one and close to the TVCN consensus near the middle of the guidance envelope. At days 4 and 5 the global models have shown run-to-run inconsistency about the details of Madeline's track near the Hawaiian Islands. The latest runs of the ECMWF, GFS, and HWRF have shifted south, with a track south of the Big Island, while much of the rest of the guidance is farther north. The NHC track has been shifted southward a little at days 4 and 5, but lies a little north of the multi-model consensus and well north of the southerly set of models. Given the lack of consistency in the track guidance, the confidence in the track foreast late in the period is lower than usual and 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 27/2100Z 15.7N 139.3W 50 KT 60 MPH 12H 28/0600Z 16.4N 140.3W 60 KT 70 MPH 24H 28/1800Z 17.3N 141.5W 65 KT 75 MPH 36H 29/0600Z 18.3N 143.0W 70 KT 80 MPH 48H 29/1800Z 19.3N 144.5W 70 KT 80 MPH 72H 30/1800Z 20.4N 148.2W 65 KT 75 MPH 96H 31/1800Z 20.5N 152.5W 60 KT 70 MPH 120H 01/1800Z 20.0N 157.0W 50 KT 60 MPH $$ Forecaster Brennan
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