ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM HURRICANE POLO DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP172014 200 AM PDT THU SEP 18 2014 Polo has changed little in organization during the past several hours. Satellite imagery indicates a small central convective feature, with an area of outer banding over the southeastern semicircle. Satellite intensity estimates from TAFB and SAB remain 65 kt, and that is the initial intensity. The initial motion is 300/7. A mid-tropospheric ridge extending westward from northwestern mainland Mexico across the Baja California peninsula should cause the tropical cyclone to move on a west-northwestward or northwestward heading for the next several days. While the overall track forecast philosophy is unchanged, the latest track guidance has shifted to the north since the previous advisory due mainly to forecasts of a northwestward motion during the first 24-48 hours. The new forecast track lies parallel to but a little north of the previous track in best agreement with the GFS and ECMWF models. However, the new track is south of the center of the guidance envelope, as well as south of the consensus model TVCE. Analyses from CIMSS at the University of Wisconsin show that northeasterly vertical wind shear is increasing over Polo. The large-scale models forecast this to continue, with the shear becoming quite strong after 24 hours. The intensity guidance responds to these developments by forecasting Polo to be weaker than the guidance of 6 hours ago. The intensity forecast follows the trend of the previous forecast, with a little strengthening during the first 24 hours followed by weakening as Polo encounters the stronger shear and cooler water. However, the forecast intensities are lowered from 24-120 hours. It should be noted that the new forecast is at the upper-level edge of the intensity guidance, and an alternative forecast scenario is that Polo does not strengthen any more before the shear causes it to weaken. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 16.7N 105.0W 65 KT 75 MPH 12H 18/1800Z 17.4N 105.8W 70 KT 80 MPH 24H 19/0600Z 18.2N 106.8W 75 KT 85 MPH 36H 19/1800Z 18.9N 107.8W 75 KT 85 MPH 48H 20/0600Z 19.6N 108.8W 70 KT 80 MPH 72H 21/0600Z 21.0N 111.0W 60 KT 70 MPH 96H 22/0600Z 22.0N 113.0W 50 KT 60 MPH 120H 23/0600Z 22.5N 115.0W 40 KT 45 MPH $$ Forecaster Beven NNNN