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Tropical Storm Octave Forecast Discussion Number 4
2019-10-18 16:47:26| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Fri Oct 18 2019 000 WTPZ43 KNHC 181447 TCDEP3 Tropical Storm Octave Discussion Number 4 NWS National Hurricane Center Miami FL EP182019 800 AM PDT Fri Oct 18 2019 A 0941 UTC GCOM microwave overpass was instrumental in showing that Octave's center is located to the east of the main convective mass, and also well to the east of a more notable mid-level circulation. Cloud tops have warmed during the past few hours, but the initial intensity is being held at 40 kt based on ASCAT data from overnight. The microwave data and recent conventional imagery show that Octave is at least partially separating from the Intertropical Convergence Zone (ITCZ). The initial motion estimate is now slowly northward, or 360/2 kt. Any additional northward progress is likely to be hindered in 24-36 hours due to the push of low-level northerly winds in the wake of a trough which is dropping southward over the Pacific. After that push, there is some difference between the models on whether Octave moves eastward or westward, so the NHC forecast continues to show a meandering or slow looping motion during the 5-day forecast period. With Octave now moving out of the ITCZ, low-level dry air to the west is wrapping into the cyclone's circulation, which is likely causing the recent waning of convection. SHIPS model diagnostics indicate that mid-level relative humidity is currently 40-50 percent, and these values are expected to decrease to 30 percent or lower in about 48 hours. This decrease in moisture will also coincide with an increase in southeasterly shear, and both factors will likely contribute to a decrease in intensity--and a loss of tropical cyclone status--during the next couple of days. The new NHC forecast closely follows the IVCN and HCCA aids and shows weakening during the next day or two, with Octave likely to degenerate into a remnant low within 48 hours. The low is expected to linger for several more days after that, but the environment does not appear conducive for regeneration into a tropical cyclone. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 10.6N 126.6W 40 KT 45 MPH 12H 19/0000Z 11.1N 126.5W 40 KT 45 MPH 24H 19/1200Z 11.6N 126.3W 35 KT 40 MPH 36H 20/0000Z 11.6N 125.9W 30 KT 35 MPH 48H 20/1200Z 11.2N 125.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 21/1200Z 11.0N 126.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 22/1200Z 11.5N 126.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 23/1200Z 12.5N 127.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg
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