AXPZ20 KNHC 220945

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
730 UTC Tue May 22 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 0915 UTC.


The monsoon trough extends from 09N84W to 09N106W to 08N129W. The ITCZ extends from 08N129W to beyond 08N140W. Scattered moderate to strong convection is observed within 195 nm on either side of monsoon trough and E of 90W. Scattered moderate is within 75 nm on either side of the axes for the remainder of the area.



Latest scatterometer data depicts moderate to fresh NW winds across the offshore waters of Baja California, where seas are running 5-7 ft. Strong SW cross equatorial swell is moving into the regional waters 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 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 broad low pressure center is developing in the far N portions near 31N114W. 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 through mid week. Large SW swell will keep seas in excess of 8 ft across the waters of southern Mexico and the open waters off Baja California today, 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 today, then moderate to fresh gap winds will pulse briefly as sharp troughing shifts slowly NW across southeast Mexico.


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 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 5-7 ft are expected through tonight 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 through tonight, 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.


A ridge extends from 1024 high pressure centered near 31N140W through the Revillagigedo Islands. Latest scatterometer data indicated fresh trade winds from 10N to 20N to the west of 130W, 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 116W. 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 the trade winds especially near a developing weak low pressure along the monsoon trough near 11N126W. Latest 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 today. Looking ahead, the upper-level pattern will amplify by mid week, supporting development of another weak low along the monsoon trough west of 125W.