000 WTPZ44 KNHC 301436 TCDEP4 TROPICAL STORM GUILLERMO DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092015 800 AM PDT THU JUL 30 2015 Guillermo's convective pattern continues to improve, with a solid band curving about half way around the center of circulation. Dvorak classifications were T3.0/45 kt from TAFB and T2.5/35 kt from SAB, and the initial intensity is therefore set at 40 kt. This could be somewhat conservative, given that the latest objective ADTs are around 45 kt. The environment ahead of Guillermo looks plenty favorable for continued strengthening. Upper-level outflow is expanding around the cyclone, and Guillermo should remain in a light-shear environment for at least the next 3-4 days. In addition, sea surface temperatures are about 29 degrees C, and the atmosphere is moist and unstable. Additional strengthening is anticipated during the next few days, and there remains a 1 in 3 chance of rapid intensification during the next 24 hours. Given the favorable environment, the official intensity forecast is a little above the intensity consensus for the entire forecast period. It should be noted that the HWRF model shows a stronger hurricane than is indicated in the official forecast, bringing Guillermo to category 2 strength in about 3 days. Some weakening should occur by days 4 and 5, mainly due to increased shear and lower oceanic heat content. Guillermo is moving west-northwestward, or 290/11 kt, to the south of the subtropical ridge. The global models indicate that a mid- to upper-level low located about 1000 miles west of southern California will deepen and amplify during the next few days, which should produce a break in the subtropical ridge. The track models are in good agreement during the first 48 hours, and most of the spread beyond that time is due to speed differences. An overall westward shift in the guidance envelope necessitated an adjustment to the official track forecast from 48 hours and beyond, and it lies close to a consensus of the GFS and ECMWF models. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 9.1N 127.5W 40 KT 45 MPH 12H 31/0000Z 9.9N 129.5W 55 KT 65 MPH 24H 31/1200Z 11.0N 132.5W 65 KT 75 MPH 36H 01/0000Z 12.0N 135.7W 70 KT 80 MPH 48H 01/1200Z 12.8N 138.6W 80 KT 90 MPH 72H 02/1200Z 14.6N 142.8W 80 KT 90 MPH 96H 03/1200Z 16.0N 145.5W 70 KT 80 MPH 120H 04/1200Z 18.0N 148.0W 60 KT 70 MPH $$ Forecaster Berg