000 AXPZ20 KNHC 271455 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 UTC Fri Sep 27 2019 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 1200 UTC surface analysis and satellite imagery through 1445 UTC. ...SPECIAL FEATURES... An elongated trough of low pressure meanders form NW Colombia northwestward to across southern Nicaragua and northern Costa Rica, and continues northwestward to low pressure of 1006 mb in the Gulf of Tehuantepec near 15N94W, then westward from there to a weakening low pressure center of 1007 mb near 16N09W. Strong W to SW surface to low-level winds were noted on an overnight Ascat pass to be situated south of this trough, roughly from 08.5N to 14N between 91W and 106W. This strong monsoonal wind flow is transporting abundant tropical moisture into the near and offshore waters of southern and southwestern Mexico, and is fueling clusters of strong thunderstorms form 10N to the Mexican coast from just east of Acapulco to the border of Mexico and Guatemala. Similar activity is seen from 14N to 17N between 101W and 105W. Strong thunderstorms producing very heavy rainfall will continue across this area during the next 24 hours and affect the coastal zones and western slopes of the Sierra Madre Occidentales. Heavy rainfall amounts could produce areas of flash flooding and landslides from Oaxaca to Michoacan through the weekend. Please refer to local weather information issued by the Mexican Meteorological Service. In addition, the 1006 mb low pressure near 15N94W is forecast to likely to become a tropical depression or storm over the weekend or early next week while it moves west-northwestward to northwestward near 13 kt near or along the southern and southwestern coasts of Mexico. Regardless of development, heavy rainfall, with the possibility of flash flooding and mudslides, is likely along the Pacific coasts of Central America and southern and SW Mexico during the next several days. This developing low pressure system has a medium chance of becoming a tropical cyclone during the next 48 hours and a high chance of becoming a tropical cyclone during the next 5 days. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 12N86W to low pressure near 15N94W 1006 mb to 15N102W to low pressure near 16N109W to 15N120W to 12N130W and to beyond 11N140W. Numerous strong convection is within 120 nm south and 60 nm north of trough between 98W and 101W. Scattered to numerous moderate strong convection is within 180 nm south of trough between 91W and 98W and within 60 nm of trough between 101W and 106W. Scattered moderate convection is within 60 nm south of trough between 123W and 134W and also between 137W and 140W. OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Overnight scatterometer data revealed light to gentle winds across the Baja California Norte offshore waters, while fresh northwest winds were observed south of Punta Eugenia to Cabo San Lucas. Wave heights are generally 4-7 ft in northwest swell across these waters. Farther south and southeast, moderate to fresh northwest winds are evident from the entrance to the Gulf of California to Acapulco then became moderate westerly winds to the Gulf of Tehuantepec. Overnight scatterometer winds also captured a low pressure center near 17N110W, where 20-25 kt were seen within 75 nm across the western semicircle. This low is moving quickly southeastward and it is embedded in the mean westerly low level wind flow across the region. High pressure behind a weakening cold front will build weakly across the Baja waters over the weekend, with the resultant gradient leading to a freshening of the northwest wind flow across the Baja California Norte waters. This is expected to build the northwest swell. Little change in the pattern is expected elsewhere to the north of Cabo Corrientes over the weekend. Winds and seas occurring south of the monsoon trough will lift northward with the developing low pressure system described above, and will also be accompanied by increasing strong thunderstorm activity. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Fresh southwest to west monsoon flow will support showers and thunderstorms off the coasts of Guatemala and El Salvador today through Sat, as it will be further enhanced by the low pressure of 1006 mb in the Gulf of Tehuantepec near 15N94W. Offshore wave heights will build to 7-9 ft today, with wave heights peaking to 8 ft spreading eastward towards the coastal waters of Nicaragua and northern Costa Rica tonight through the weekend. REMAINDER OF THE AREA... Light to moderate northeast trade winds will persist north of 17N and west of 130W for the next couple days. Elsewhere, long-period north swell is producing 7 to 10 ft seas roughly north of 27N and west of 120W, based on the latest altimeter data passes from overnight last night. With the swell energy gradually dissipating through Sun, this will result in a decay of the wave heights to 8 ft by early on Sun. A cold front is forecast to drop southward into the northern waters and weaken this weekend. Expect moderate to fresh northeast winds to develop north of 26N and west of 125W on Sun following frontal passage. $$ Aguirre