ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM Tropical Storm Guillermo Discussion Number 6 NWS National Hurricane Center Miami FL EP072021 300 PM MDT Sun Jul 18 2021 Guillermo's convective pattern has not changed significantly since early this morning, but an ASCAT overpass just after 1600 UTC revealed that its wind field has expanded. The maximum winds in the ASCAT data were a little above 45 kt, so the initial intensity has been increased to 50 kt accordingly. This is just above the latest Dvorak estimates from TAFB and SAB. A slight additional increase in the maximum winds appears likely during the next day or so, owing to favorable environmental conditions. However, the highly asymmetric structure of Guillermo and its relatively broad inner-core will continue to be limiting factors. In about 24 to 36 h, Guillermo will begin to move over waters colder than 26 deg C, and this should cause the tropical storm to gradually weaken. After about 72 h, a drier and more stable environment will likely also contribute to weakening. Despite those factors, the GFS and HWRF models continue to indicate that Guillermo could maintain at least some deep convection through the full 5-day period. The NHC forecast therefore carries Guillermo as a tropical cyclone through day 5, but it would not be surprising if it became a remnant low sooner than that. The official intensity forecast is slightly higher than the intensity consensus, near the SHIPS and GFS forecasts. The aforementioned ASCAT data indicated that Guillermo is centered slightly north of previous estimates and the estimated initial motion is slightly faster than the previous advisory, at 290/ 12 kt. The NHC track forecast has been adjusted northward and faster as a result, but the overall reasoning remains the same. A mid-level ridge to the north of Guillermo will likely steer the tropical storm westward beginning tonight. Guillermo should then continue generally westward for the next several days. A slight west-southwestward bend is possible late in the forecast period as the cyclone weakens and becomes primarily steered by low-level flow. The official track forecast is heavily based on the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 18.7N 113.8W 50 KT 60 MPH 12H 19/0600Z 19.0N 115.7W 55 KT 65 MPH 24H 19/1800Z 19.1N 118.4W 55 KT 65 MPH 36H 20/0600Z 19.0N 121.3W 55 KT 65 MPH 48H 20/1800Z 19.0N 124.2W 50 KT 60 MPH 60H 21/0600Z 18.9N 127.1W 45 KT 50 MPH 72H 21/1800Z 18.6N 129.8W 40 KT 45 MPH 96H 22/1800Z 18.2N 135.0W 35 KT 40 MPH 120H 23/1800Z 18.0N 140.0W 30 KT 35 MPH $$ Forecaster Zelinsky NNNN