000 AXPZ20 KNHC 212143 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Mon May 21 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 2030 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 09.5N74W TO 11N94W TO 09.5N115W TO 08N133W. The ITCZ extends from 08N134W to beyond 09.5N140W. Scattered moderate to strong convection is observed from 04.5N to 11N between the coast of Colombia and 100W. Widely scattered moderate isolated strong is noted from 05N to 11.5N between 100W and 124W. Widely scattered moderate to strong is noted within 180 nm N of the axis between 133W and 140W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Early afternoon scatterometer data continue to show moderate to fresh NW winds across the offshore waters of Baja California, where seas are running 5-7 ft. Strong SW cross equatorial swell has begun to move into the regional waters today and is producing seas of 7-8 ft from 21N to 23N between Las Islas Tres Marias and 112W. This swell will penetrate southern portions of the Gulf of California this afternoon through early Wed. Generally light to gentle variable winds are noted over the southern half of Gulf of California, while moderate S to SW winds prevail across the north half as a low pressure center has developed in the far N portions near 31N114.5W. Light NW to W winds continue farther south across the Mexican coastal waters. As mentioned in recent days, the main marine forecast issue for the next couple of days is the arrival of long period SW swell moving into all of the regional Pacific waters today through mid week. Large SW swell will begin to raise seas in excess of 8 ft across the waters of southern Mexico today, and the open waters off Baja California tonight and Tue, as it mixes with NW swell off Baja California Norte. Overnight and morning altimeter data suggests that the largest and strongest swell is aimed for central Mexico between Tehuantepec and Mazatlan. In the Gulf of Tehuantepec, light winds will persist into Tue, then moderate to fresh gap winds will pulse briefly as sharp troughing shifts slowly NW across southeast Mexico. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Light to gentle winds will dominate the gulf the entire forecast period as elongated weak low pressure will prevail across Central America. Seas of 5-7 ft this afternoon are forecast to build to 6-9 ft over the Gulf and nearby waters through mid week due to the strong long period SW swell arriving today. Gulf of Panama: Gentle to moderate S to SW winds are forecast through mid week. Seas of 4-6 ft in long period SW swell today will build to 5-7 ft tonight through late Tue as the SW swell reaches the coasts of Panama and Colombia. Elsewhere, gentle to moderate SW winds are expected to the south of the monsoon trough with light to gentle variable winds north of trough as a weak pressure pattern remains over Central America. Seas of 6-9 ft in building long period SW swell west of the Galapagos Islands are expected to propagate northward tonight through late Tue, building to 8 to 11 ft to the west and northwest of the Galapagos Islands tonight. Additionally, deep layered upper troughing extending from the Gulf of Mexico southward into the western Caribbean will drift westward and dig farther southward into Central America Wed and Thu. This may induce a broad low level cyclonic circulation across portions of the Yucatan and Central America, leading to periods of heavy rainfall across the region. This heavy rain could extend into the Pacific coastal zones of the region from Wed through Fri. REMAINDER OF THE AREA... A ridge extends from 1026 high pressure centered near 31N141W through the Revillagigedo Islands. Afternoon scatterometer data indicated fresh to strong trade winds from 10N to 22N to the west of 127W, between the ridge and lower pressure along the monsoon trough and ITCZ. Elsewhere the ridge is maintaining generally moderate to fresh trades north of the monsoon trough and west of 113W. Convergence of these winds with light to moderate SW flow on the south side of the monsoon trough is supporting clusters of showers and thunderstorms near the monsoon trough west of 110W. Various overnight altimeter data also indicated 5 to 7 ft seas north of 20N where winds are lighter, and 7 to 9 ft seas in the trade wind belt between the monsoon trough as far north as 17N as SW swell is moving into the regional waters. The ridge will build north of 20N into mid week, enhancing trade winds especially near a developing weak low pressure along the monsoon trough near 11N126W. Various recent altimeter satellite passes continue to show SW swell in excess of 10 ft south of 10N, propagating northward. This will overtake the region east of 130W through Tue. Looking ahead, the upper pattern will amplify by mid week, supporting development of another weak low along the monsoon trough west of 125W. $$ Stripling