221 WTPZ42 KNHC 012055 TCDEP2 Tropical Depression Seventeen-E Discussion Number 4 NWS National Hurricane Center Miami FL EP172018 300 PM MDT Sat Sep 01 2018 ASCAT scatterometer overpasses at 1625Z and 1704Z indicated that the depression's inner-core wind field remains elongated northeast-to-southwest, with a second fully exposed low-level swirl located near the northeastern end of the wind field. There was also a fairly large field of 27-29 kt surface wind vectors located in the southern quadrant. Various Dvorak satellite intensity estimates have remained unchanged since the previous advisory, so the initial intensity is being held at 30 kt for this advisory. The initial motion estimate is an uncertain 285/10 kt. Most of the global and regional models take the cyclone west-northwestward for the next 24 h or so, and then move it westward thereafter. The exception is the new GFS model run, which takes the system northward for 36 h before turning it back westward. The GFS appears to have keyed in on the aforementioned exposed low-level swirl noted in the ASCAT and recent visible satellite data, and makes it the primary circulation center. The official forecast track calls for the main low-level center to remain/develop closer to the stronger deep convection and strongest low-level winds and associated vorticity. The more northern track of the GFS model is being discounted, but it has strongly skewed the various consensus tracks farther to the north. As a result, the new official forecast track lies south of the consensus model HCCA, and is close to the previous advisory track and a blend of the more westerly HWRF and ECMWF models. Due to the GFS model's more northerly track, the GFS-based shear computations have a high bias. In contrast, the more southerly ECMWF model has continued to forecast much weaker shear of 10-15 kt for the next 72 h, followed by decreasing shear after that. These more modest shear conditions, combined with very warm SSTs greater than 28.5 deg C, should allow for at least steady strengthening to occur. The only hindering factor early on remains when the inner-core wind field contracts down and becomes better defined, which would result in sooner and more significant intensification to occur than is indicated by the official forecast. For now, the intensity forecast remains above the consensus models HCCA and IVCN due to the very low bias induced by the GFS-based SHIPS and LGEM intensity models. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 14.9N 111.1W 30 KT 35 MPH 12H 02/0600Z 15.3N 111.6W 35 KT 40 MPH 24H 02/1800Z 15.7N 112.5W 40 KT 45 MPH 36H 03/0600Z 16.0N 113.7W 45 KT 50 MPH 48H 03/1800Z 16.2N 115.1W 55 KT 65 MPH 72H 04/1800Z 16.3N 118.3W 75 KT 85 MPH 96H 05/1800Z 16.9N 122.4W 85 KT 100 MPH 120H 06/1800Z 18.3N 127.3W 95 KT 110 MPH $$ Forecaster Stewart