WTPZ44 KNHC 010833

200 AM PDT SAT AUG 01 2015

Guillermo's cloud pattern has changed little in organization over the past several hours. Convective banding features are not as well defined as they were 24 hours ago, and the CDO lacks a circular shape. Dvorak T-numbers remain unchanged from the previous advisory package, so the intensity estimate is held at 90 kt. Upper-level outflow has become restricted to the northwest of the cyclone. The oceanic and atmospheric environment is not likely to become more conducive for strengthening over the next couple of days, and the numerical intensity guidance generally shows a gradual weakening trend. Near the end of the forecast period, global models indicate a significant increase in vertical shear associated with strong upper-tropospheric westerlies near the Hawaiian Islands. The official forecast is near or slightly above the intensity model consensus and shows, as in the previous advisory, weakening to tropical storm status in 96 hours.

Based on geostationary and microwave center fixes, in particular an earlier SSMI/S pass from 0424Z, the motion has slowed somewhat and is now estimated to be about 285/14 kt. Guillermo is approaching a weakness in the zonally-oriented mid-level ridge to its north, and this should result in further deceleration over the next couple of days. In 3-5 days, the steering currents become less well defined in the global models and there is a fair amount of spread in the dynamical track predictions. The ECMWF model has been doing a bit of a flip-flop in its last few runs, and it has shifted back the south after shifting northward in the previous run. The official forecast is held very close to the previous NHC track and is close to the latest track model consensus, TVCN, which combines not only the GFS and ECMWF solutions but also the HWRF, GFDL, and U.K. Met. Office model forecasts.

Due to uncertainties in longer-range track predictions, it is important for users not to focus on the exact track forecasts at 96 and 120 hours.


INIT 01/0900Z 13.4N 137.4W 90 KT 105 MPH 12H 01/1800Z 13.9N 139.6W 90 KT 105 MPH 24H 02/0600Z 14.5N 142.0W 90 KT 105 MPH 36H 02/1800Z 15.1N 144.0W 85 KT 100 MPH 48H 03/0600Z 15.8N 145.4W 75 KT 85 MPH 72H 04/0600Z 17.3N 148.0W 65 KT 75 MPH 96H 05/0600Z 19.0N 151.0W 60 KT 70 MPH 120H 06/0600Z 20.5N 154.0W 50 KT 60 MPH

$$ Forecaster Pasch