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Tropical Storm Hector Forecast Discussion Number 7
2018-08-02 10:49:22| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Thu Aug 02 2018 853 WTPZ45 KNHC 020849 TCDEP5 Tropical Storm Hector Discussion Number 7 NWS National Hurricane Center Miami FL EP102018 200 AM PDT Thu Aug 02 2018 Hector's satellite presentation has quickly improved over the past few hours. Recent microwave and scatterometer data indicate that the low-level center is now well embedded within the expanding convective canopy, and a tiny mid-level eye has formed. In fact, a late-arriving WindSat pass from around 0230 UTC showed that Hector had a mid-level structure that has been associated with rapidly intensifying tropical cyclones, when present in low-shear environments. The initial intensity has been raised to 60 kt based on a timely ASCAT-B overpass around 0556 UTC. Although the maximum winds measured by the ASCAT were only around 55 kt, at least some undersampling seems likely given the small size of the inner-core of the cyclone. The northeasterly shear that has been affecting Hector does not appear to be significantly affecting the inner-core of the cyclone at this time. However, it is uncertain whether this is only a short-term trend, or if the inner core will remain protected from the higher shear going forward. While the GFS and ECMWF indicate that the shear should decrease through today, the HWRF and HMON models forecast that Hector will become strongly sheared by tomorrow and temporarily weaken as a result. The small size of the tropical cyclone further complicates the intensity forecast since small cyclones can quickly intensify or weaken, especially in moderate shear environments, and these short-term fluctuations are very difficult to predict. As a course of least regret, the NHC forecast does not show significant strengthening or weakening for the first 48 h of the forecast and instead shows steady strengthening, similar to the DSHP and LGEM models, and is higher than the previous advisory. For days 3-5, there is a better consensus among the models that Hector will strengthen, and the official forecast is still close to the multi-model consensus and the previous forecast. The initial motion estimate is now 285/10 kt. There is more confidence in the track forecast. A strong subtropical ridge extending from the eastern Pacific into the central Pacific should keep Hector on a general west heading through the entire forecast period. The main source of uncertainty is still the speed of the tropical cyclone at days 3-5. Since the main difference between the models appears to be subtle differences in the strength of the ridge, the NHC forecast is still based on the multi-model consensus and little change has been made from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 02/0900Z 14.3N 123.4W 60 KT 70 MPH 12H 02/1800Z 14.5N 125.1W 65 KT 75 MPH 24H 03/0600Z 14.6N 127.4W 70 KT 80 MPH 36H 03/1800Z 14.5N 129.7W 75 KT 85 MPH 48H 04/0600Z 14.4N 132.0W 80 KT 90 MPH 72H 05/0600Z 14.0N 136.6W 85 KT 100 MPH 96H 06/0600Z 14.0N 141.5W 95 KT 110 MPH 120H 07/0600Z 14.5N 146.5W 95 KT 110 MPH $$ Forecaster Zelinsky
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