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Tropical Storm Lidia Forecast Discussion Number 7
2017-08-31 10:48:59| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Thu Aug 31 2017 000 WTPZ44 KNHC 310848 TCDEP4 Tropical Storm Lidia Discussion Number 7 NWS National Hurricane Center Miami FL EP142017 300 AM MDT Thu Aug 31 2017 Scatterometer data and microwave images indicate that Lidia has a deformed circulation, with what appears to be two lobes of vorticity rotating around a common center. The unmanned NASA Global Hawk flew very near the centroid of the circulation last evening and provided a better estimate of Lidia's central pressure (about 998 mb at the time). In addition, a dropsonde released to the east of the center measured a mean boundary layer wind of 45 kt, which equates to a surface wind a little over 35 kt. Assuming the dropsonde did not sample the highest winds, and given that deep convection has become more organized into two distinct clusters since that time, the initial intensity is raised to 40 kt. Lidia is moving north-northwestward, or 335/7 kt, between a mid-level high centered over central Mexico and a cyclonic gyre located to the west over the Pacific. This motion should continue for the next 36 hours, but then after that time, high pressure over the southwestern United States should force Lidia to turn northwestward and west-northwestward on days 2 through 5. Most of the spread in the track models is related to Lidia's forward speed, and there is a notable disparity between the faster GFS and slower ECMWF models. The new NHC track forecast is a little faster than the previous one to better match the speeds of the TVCN multi-model consensus and the HFIP Corrected Consensus Approach (HCCA). Even though Lidia is in an environment of low shear and over very warm waters, the storm's large size and lack of an inner core are likely to prevent fast strengthening before the center reaches the Baja California peninsula. Since the ambient environment is favorable, the NHC forecast continues to call for modest strengthening and still shows a peak intensity of 55 kt in about 24 hours, which is in line with HCCA. Weakening is expected after 24 hours due to the center moving up the spine of the Baja California peninsula, but tropical-storm-force winds are likely to spread up the Gulf of California well east of the center. Lidia is forecast to become a remnant low by day 3 due to its interaction with land, and further weakening is anticipated over the cold waters of the California Current on days 4 and 5. Lidia is a large system accompanied by very heavy rains which are already occurring over portions of western Mexico and Baja California Sur. Regardless of how strong Lidia becomes, life-threatening flash floods and mudslides will be a significant hazard over these areas. FORECAST POSITIONS AND MAX WINDS INIT 31/0900Z 21.3N 109.4W 40 KT 45 MPH 12H 31/1800Z 22.3N 109.9W 50 KT 60 MPH 24H 01/0600Z 23.6N 110.5W 55 KT 65 MPH 36H 01/1800Z 25.1N 111.4W 45 KT 50 MPH...INLAND 48H 02/0600Z 26.7N 112.6W 40 KT 45 MPH...INLAND 72H 03/0600Z 29.2N 115.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 04/0600Z 30.0N 119.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 05/0600Z 30.5N 121.5W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg
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