ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM Tropical Storm Guillermo Discussion Number 2 NWS National Hurricane Center Miami FL EP072021 300 PM MDT Sat Jul 17 2021 Fragmented convective banding has gradually increased since the previous advisory, with a very tight low-level vortex having become evident over the center in high-resolution visible satellite imagery. Low-cloud motion vectors in the inner-core region have been around 45 kt, which equals approximately 34-kt surface winds if the cloud motions represent the 925-mb level. Satellite current intensity (CI) estimates remain T2.5/35 kt from TAFB and and SAB. The latest UW-CIMSS ADT estimate is T2.2/32 kt, with the raw and adjusted T-numbers at 37 kt and 36 kt, respectively. Based on these data, the intensity has been increased to 35 kt, making the cyclone Tropical Storm Guillermo. The initial motion estimate is 295/12 kt. There are no significant changes to the previous track forecast or reasoning. The global and regional models remain in very good agreement on Guillermo moving west-northwestward today, and then turning toward the west later tonight or early Sunday, with a general westward motion continuing through day 3. By days 4 and 5, the deep-layer ridge to the north of Guillermo is forecast by the models to gradually build southward, forcing the tropical storm west-southwestward. The latest NHC model guidance has converged tightly around the previous forecast track through 96 h, so no adjustments were made. The new official forecast track lies close to the tightly packed consensus models, which are about midway between the stronger GFS track forecast on the right side of the guidance envelope and the weaker ECMWF solution on the left or south side. Guillermo is expected to remain within a low vertical wind shear regime and a moist mid-level environment, and over sea-surface temperatures (SST) of at least 27C for the next 48 hours or so. These favorable conditions should allow for at least modest strengthening to occur during that time, with the only hindering factor being Guillermo's large circulation. By 60 hours and beyond, the cyclone will be moving over sub-26C SSTs, which should induce gradual weakening despite the low vertical wind shear pattern. The new NHC intensity forecast is similar to the previous advisory, and closely follows the NOAA-HCCA corrected consensus model, which is above most of the available intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 17.1N 110.1W 35 KT 40 MPH 12H 18/0600Z 17.6N 111.7W 45 KT 50 MPH 24H 18/1800Z 18.0N 113.9W 50 KT 60 MPH 36H 19/0600Z 18.3N 116.2W 55 KT 65 MPH 48H 19/1800Z 18.4N 118.7W 55 KT 65 MPH 60H 20/0600Z 18.5N 121.2W 50 KT 60 MPH 72H 20/1800Z 18.4N 123.8W 45 KT 50 MPH 96H 21/1800Z 18.1N 128.9W 35 KT 40 MPH 120H 22/1800Z 17.8N 134.1W 30 KT 35 MPH $$ Forecaster Stewart NNNN