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Tropical Storm Hernan Forecast Discussion Number 5
2020-08-27 10:43:10| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Thu Aug 27 2020 000 WTPZ43 KNHC 270842 TCDEP3 Tropical Storm Hernan Discussion Number 5 NWS National Hurricane Center Miami FL EP132020 300 AM MDT Thu Aug 27 2020 Although Hernan is a sheared tropical cyclone, another strong burst of deep convection with cloud tops of -83C to -86C has developed near and south through west of the center. An 0401Z ASCAT-A scatterometer pass revealed several 38-40 kt surface wind vectors of south through southwest of the center, so the initial intensity has been increased to 40 kt, which is supported by a recent UW-CIMSS SATCON estimate of 40 kt. The initial motion is estimate is 355/04 kt. Hernan is expected to remain caught within a large-scale, eastern North Pacific cyclonic gyre during the next few days, which will result in Hernan moving counter-clockwise around the eastern and northern periphery of the gyre. The cyclone will continue to move slowly northward this morning, followed by a turn toward the northwest by Thursday afternoon, with a west-northwestward motion expected on Friday. By Saturday, Hernan is forecast to degenerate into a remnant low pressure system, and possibly even dissipate and merge with Tropical Storm Iselle when the two systems are west-southwest of Baja California. The new NHC track is a very similar to the previous advisory track, and lies close to a blend of the simple track consensus models TVCE and GFEX, and the NOAA-HCCA corrected-consensus model. Hernan will remain in a moderate-to-strong easterly vertical wind shear regime for the next three days, which is expected to prevent any significant strengthening from occurring despite the cyclone being over warm waters and within a moist mid-level environment. By 60 hours, Hernan is forecast to degenerate into a remnant low, and possibly merge with Tropical Storm Iselle in 72-96 hours. The official intensity forecast is similar to the IVCN intensity consensus model. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 18.6N 106.0W 40 KT 45 MPH 12H 27/1800Z 19.5N 106.2W 40 KT 45 MPH 24H 28/0600Z 20.7N 107.3W 40 KT 45 MPH 36H 28/1800Z 21.9N 108.8W 35 KT 40 MPH 48H 29/0600Z 22.7N 110.8W 30 KT 35 MPH 60H 29/1800Z 22.7N 112.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 30/0600Z 22.4N 114.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 31/0600Z...DISSIPATED $$ Forecaster Stewart
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