811 AXPZ20 KNHC 280920 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Fri Sep 28 2018 Tropical Weather Discussion for the eastern Pacific Ocean from the Equator to 32N, east of 140W. The following information is based on satellite imagery, weather observations, radar, and meteorological analysis. Based on 0600 UTC surface analysis and satellite imagery through 0900 UTC. ...SPECIAL FEATURES... Hurricane Rosa is centered near 16.9N 117.4W at 0300 UTC or 555 nm SW of the southern tip of Baja California, moving W at 6 kt. Estimated minimum central pressure is 940 mb. Maximum sustained winds are 125 kt with gusts to 150 kt. Numerous moderate to strong convection is within 180 nm of the center. Scattered moderate isolated strong convection is elsewhere within 300 nm of the eye. Swells generated by Rosa will affect western Mexico, including the Baja California peninsula, and southern California during the weekend, and may cause life-threatening surf and rip current conditions. Please consult forecasts from your local weather office. See latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP5/WTPZ25 KNHC for more details. An 1007 mb area of low pressure near 11N97W is poorly organized with a broad cyclonic circulation. Scattered moderate isolated strong convection is from 07N to 11N between 91W and 99W. Fresh easterly winds and seas to 9 ft are in the N semicircle of the low within 180 nm. This low will drift WNW and gradually become better organized through tonight. Environmental conditions are conducive for development, and a tropical cyclone is expected to form this weekend. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 10N85W to low pressure near 11N97W to 12N104W, then resumes from 13N121W to 09N132W to 10N140W. Scattered moderate convection is within 15 nm N and 75 nm S of the trough axis between 121W and 133W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... See Special Features above for information on Hurricane Rosa and the tropical low near 11N97W. A ridge along 27N will retreat ahead of Hurricane Rosa. Gentle to moderate NW flow west of the Baja peninsula will become northerly on Sat, with marine conditions deteriorating across southern waters by Sat night as Rosa approaches the area, with hurricane or tropical storm conditions spreading NE into the waters W of Baja California Norte through early next week. In the Gulf of California, light to gentle southerly winds are expected through Sun night. The southerly flow will increase to near gale force N of 27N thereafter, with tropical storm conditions possible N of 29N Mon night and Tue from Rosa. In the Gulf of Tehuantepec, nocturnal offshore northerly flow will pulse to fresh the next several days with seas building to 7 ft during strongest winds. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Numerous showers and scattered thunderstorms are likely in the the waters off Guatemala and El Salvador through early Sat. The monsoon trough will meander between 09N and 12N through Tue, with gentle to moderate winds expected on either side of the trough axis. Moderate to fresh E nocturnal drainage flow is expected in the Gulf of Papagayo through Sun night. REMAINDER OF THE AREA... See Special Features above for information on Hurricane Rosa. A broad ridge extends along 27N with gentle anticyclonic flow N of the ridge, and moderate to fresh trades S of 23N. A series of weak cold fronts or troughs will sweep across the far NW waters through the weekend, accompanied by a W to NW wind shift. NW swell may propagate into the N central waters early next week. $$ Mundell