000 AXPZ20 KNHC 181945 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Tue May 18 2021 Tropical Weather Discussion for the eastern Pacific Ocean from 03.4S to 30N, east of 120W including the Gulf of California, and from the Equator to 30N, between 120W and 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. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 08N78W to 10N90W to 10N115W. The ITCZ extends from 10N115W to 06N125W to 09N140W. Scattered moderate convection is noted from 03N to 07N east of 84W. Scattered moderate to isolated strong from 06N to 10N between 92W and 104W. Scattered moderate convection is noted from 04N to 07N between 118W and 122W, from 09N to 12N between 122W and 129W, and from 10N to 13N between 132W and 135W. OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A ridge extends from high pressure centered near 35N145W southeastward toward Socorro Island. A recent scatterometer satellite pass indicated moderate to fresh NW winds off the coast of Baja California, between the ridge and troughing over northwest Mexico. An altimeter satellite pass from a few hours ago indicated seas are mostly 5 to 7 ft off Baja California. Light breezes and slight seas are noted over the Gulf of California. Farther south, another scatterometer pass indicated light to gentle W to NW winds are evident over the offshore waters of southern Mexico, south of 20N. A concurrent altimeter pass showed seas of 5 to 7 ft as well. This is likely due to ongoing longer period SW swell. For the forecast, the high pressure centered west of Baja California will continue to support mainly moderate to fresh NW winds north of Cabo San Lazaro into Thu. Winds will increase to fresh to strong speeds mainly west of central and northern Baja California and over the northern Gulf of California late Thu into Fri as stronger high pressure builds southeastward across the waters west of Baja California behind a weak frontal boundary moving across southern California and the far northern Baja California Norte. Meanwhile, long period SW swell will persist over Mexican offshore waters, especially south of Cabo Corrientes, with another set arriving by Fri. Looking ahead, a trough or low may form well south of the Gulf of Tehuantepec region. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, and WITHIN 750 NM OF ECUADOR... A recent scatterometer pass confirmed moderate NE to E gap winds in the Gulf of Papagayo. A concurrent altimeter satellite pass showed 5 to 7 ft seas, approaching 8 ft in the gap wind plume. These seas include a dominant component of long period SW swell, which is supporting mainly 5 to 7 ft seas across the offshore areas across the region. The upper level pattern is supporting a few showers and thunderstorms along the monsoon trough, impacting the waters off western Panama and beyond 180 nm off the coasts of Nicaragua, El Salvador, and Guatemala. For the forecast, seas of 5-7 ft will change little into late in the week. Long period cross- equatorial southerly swell will continue to impact the offshore forecast waters through Fri night, then begin to subside on Sat. Seas between Ecuador and the Galapagos Islands will begin to build to 8 ft or higher on Wed as additional pulses of long- period southwest swell begin to propagate through those waters. Looking ahead, fresh gap winds are possible through the Gulf of Papagayo by Sat. REMAINDER OF THE AREA... High pressure ridging continues to dominate the waters north of 15N. The pressure gradient between it and comparatively lower pressures in the tropical zone area is leading to a large area of moderate to fresh trade winds north of the ITCZ, with seas up to 8 ft. Gentle to moderate trade winds are noted elsewhere, with seas in the range of 6-7 ft mainly due to a southerly swell component. By late Fri, the area of moderate to fresh trade winds will have expanded to encompass the waters west of a line from 21N116W to 08N129W as the high pressure over the region strengthens. Long period cross-equatorial southerly swell over the waters south of about 11N and east of about 110W, except in the lee of the Galapagos Islands will be replaced by a new set of long- period southerly swell beginning today. This new set of southerly swell will propagate through these same waters through late Wed night, then begin to decay through Fri night. Before doing so, it is expected to raise seas to a peak of 10 or 11 ft over the far south-central waters west of the Galapagos Islands. $$ Christensen