168 AXPZ20 KNHC 302044 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2042 UTC Sun Sep 30 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 1800 UTC surface analysis and satellite imagery through 2100 UTC. ...SPECIAL FEATURES... Hurricane Rosa centered near 25.2N 118.1W at 30/2100 UTC or 230 nm SW of Punta Eugenia Mexico moving NNE at 10 kt. Estimated minimum central pressure is 982 mb. Maximum sustained wind speed is 65 kt with gusts to 80 kt. Dry air is entraining into the hurricane. Scattered moderate convection is within 90 nm in the northern semicircle of Rosa, with no convection in the southern semicircle. Rosa is expected to weaken to a tropical storm this evening, then continue northeast before making landfall over Baja California Norte late Mon. Rosa will then weaken further to depression Mon night into early Tue as it moves across the far northern Gulf of California. Flooding rains from Rosa are expected across northwest Mexico and the southwest United States over the next few days. Swells generated by Rosa will affect portions of the coasts of southwestern Mexico, most of the west coast of the Baja California peninsula, and southern California through Tuesday. These swells are likely to cause life- threatening surf and rip current conditions. See latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP5/WTPZ25 KNHC for more details. Farther south, Tropical Storm Sergio centered near 11.5N 106.3W at 30/2100 UTC or 460 nm SSW of Manzanillo Mexico moving W at 11 kt. Estimated minimum central pressure is 998 mb. Maximum sustained wind speed is 55 kt with gusts to 65 kt. Sergio is expected to continue to intensify and reach hurricane strength by late today as it continues westward and away from the coast of Mexico. Sergio is expected to reach major hurricane strength by early Tue as it starts moving more the northwest. See latest NHC forecast/advisory under AWIPS/WMO headers MIATCMEP1/WTPZ21 KNHC for more details. ...TROPICAL WAVES... A tropical wave extends along 96W north of 04N into southern Mexico just west of the Gulf of Tehuantepec. No significant convection is noted. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A segment of the monsoon trough extends from 08N78W to 11N96W. Another segment of the monsoon trough reaches from 17N117W to 13N128W, where it transitions to the intertropical convergence zone and continues to 10N140W. Scattered moderate convection is noted from 06N to 08N between 84W and 86W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... See Special Features above for information on Hurricane Rosa and Tropical Storm Sergio. Swell associated with Rosa will continue to propagate across the offshore forecast waters W of Baja California. Seas in the form of mixed swell in excess of 8 ft are observed in earlier altimeter satellite passes over most of the ocean from 10N to 28N between 110W and 130W and north of Sergio toward Cabo Corrientes. In the Gulf of California, gentle to moderate southerly winds are expected through tonight. The southerly flow will increase to near gale force N of 27N Mon, with seas building to around 11 ft late Mon north of Tiburon Island. Tropical storm conditions from Rosa are possible across the northern Gulf of California Mon and Mon night. Winds and seas will diminish rapidly thereafter over the northern Gulf of California through late Tue. In the Gulf of Tehuantepec, an earlier scatterometer pass captured fresh to strong gap winds. These pulses will persist tonight and Mon night in the wake of a tropical wave moving past the area, and also in response to tight pressure gradient across the isthmus of Tehuantepec. Seas will be 5 to 7 ft through most of the day with a component of southerly swell generated from Sergio well to the west of the region. These seas will build to 8 or 9 ft with added pulse of gap winds during the overnight hours. The , with seas building to 9 or 10 ft, mainly during the overnight and early morning hours. These marine conditions are expected to persist through mid week. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... The monsoon trough will meander between 09N and 12N through Thu, 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 tonight. REMAINDER OF THE AREA... See Special Features above for information on Hurricane Rosa and Tropical Storm Sergio. A pre-frontal trough has entered the forecast waters east of 140W and south of 32N, weakening the subtropical ridge across the waters north of 20N. A weak cold front will follow behind the trough this evening, and eventually sweep across the waters north of 20N through mid week as it weakens further. This will keep trade wind flow minimal farther south into the deep tropics. Long period NW swell will follow the front, eventually mixing with the mixed swell generated from Rosa through mid week. This swell also eventually mix with southeasterly swell generated from Sergio as it moves farther northwest. This pattern will leave the entire region north of 15N in mixed swell greater than 8 ft by mid week, reaching as far east as the entrances to the Gulf of California. $$ Christensen