ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM Tropical Storm Lowell Discussion Number 5 NWS National Hurricane Center Miami FL EP172020 300 PM MDT Mon Sep 21 2020 Tropical Depression Seventeen-E has continued to have a ragged appearance in satellite imagery during the day. The circulation is elongated, with the main center just northeast of a poorly organized convective mass and a secondary vorticity maximum well to the north-northeast near Socorro Island. However, recent scatterometer data showed an area of 35-40 kt winds to the south and southeast of the main center. Based on this, the depression is upgraded to Tropical Storm Lowell with an initial intensity of 40 kt. The initial motion is now 290/14 kt. There are no significant changes in the track forecast philosophy, the track forecast guidance, or the track forecast since the last advisory. Lowell is being steered by a large low- to mid-level ridge to the north and northwest, and this ridge is forecast to persist through the forecast period. The track guidance shows that the system should continue west-northwestward for about 36 h, followed by a westward motion through 120 h. The track guidance is still very tightly clustered, and the new forecast track is near the various consensus models. Lowell is still experiencing some easterly shear, which the models suggest should abate some in the next 12 h or so. However, the poor organization of the storm suggests it may take a while to respond to the more favorable environment. Thus, the new intensity forecast continues the trend of the old forecast in showing slow strengthening for the first 36-48 h. After that time, the intensity will be strongly dependent on where the center is in relation to the strong sea-surface temperature gradient. Since the forecast track is basically unchanged, the new intensity forecast has only minor tweaks from the previous forecast based on the forecast track keeping the system over 25-26C water temperatures through 120 h. However, any motion north of the forecast track would bring the center over colder water and lead to a system weaker than forecast, while any motion south of the track would keep it over warmer water and possibly allow the cyclone to become a hurricane. The intensity forecast remains low confidence. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 17.4N 113.6W 40 KT 45 MPH 12H 22/0600Z 18.3N 115.2W 45 KT 50 MPH 24H 22/1800Z 19.2N 117.5W 50 KT 60 MPH 36H 23/0600Z 19.8N 119.4W 55 KT 65 MPH 48H 23/1800Z 20.2N 121.1W 60 KT 70 MPH 60H 24/0600Z 20.5N 122.8W 60 KT 70 MPH 72H 24/1800Z 20.5N 124.4W 60 KT 70 MPH 96H 25/1800Z 20.5N 128.0W 60 KT 70 MPH 120H 26/1800Z 20.5N 131.5W 50 KT 60 MPH $$ Forecaster Beven NNNN