AXPZ20 KNHC 312125

2205 UTC TUE MAY 31 2016

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.


Tropical wave is moving off Costa Rica. Scattered convection is noted from 05N to 08N between 83W and 87W.

Tropical wave is along 97W from 05N to !3N. This wave is moving into an area of strong southwest winds, as noted in earlier scatterometer data. Low level convergence due to these winds is supporting a large area of scattered to numerous shower and thunderstorms from 07N to 11N between 92W and 103W.


The monsoon trough extends from 10N86W to 09N90W to 11N100W. It then continues to a low pressure area near 09N110W, then farther west to another low pressure system centered near 10N116W before transitioning to the ITCZ near 08N121W. The ITCZ continues to 07N135W then beyond 07N140W. Scattered moderate to isolated strong convection is noted within 180 nm south of the monsoon trough between 85W and 105W.


North of 15N east of 120W - an upper trough is cutting across the northern reaches of the Gulf of California. A related surface trough extends across the Baja California peninsula. The interaction between the subtropical ridge is maintaining a tight pressure gradient, with resultant fresh to strong northwest winds off the southern tip of the Baja California peninsula, as noted in a 11Z Rapidscat pass. These winds will diminish tonight as the trough shifts east. Altimeter data from this morning indicated seas 8 to 9 ft south of 20N, in predominantly southwest swell mixed with northwest swell. This swell is expected to decay below 8 ft through Wednesday.

South of 15N east of 120W - successive scatterometer passes since last night have indicated a surge of southwest winds into the monsoon trough north of 04N between roughly 90W and 115W. Altimeter data from this area has been showing concurrent wave heights of 8 to 9 ft, with some contribution of southwest swell. The winds are to the east of a pair of elongated weak low pressure areas along the monsoon trough farther west near 110W and 116W. The winds are expected to diminish after Wednesday as the low pressure areas drift farther west, allowing seas and thunderstorm activity to diminish as well.

West of 110W - A cold front is approaching the waters north of 25N to the east of 140W. Although strong winds are noted just ahead of this front, the front will weaken and stall before crossing into the discussion area through tonight. Wave heights of 6 to 7 ft will impact the waters north of 25N and west of 137W through Wednesday related to shorter period swell generated along the front. Otherwise, broad ridging will prevail across the waters north of 15N and west of 120W. Farther south into the tropics, a pair of weak low pressure centered along the monsoon trough and near 110W and 116W respectively will gradually merge and deepen through Wednesday, crossing 120W by late Friday. No tropical cyclone development is expected through mid week, but the merged low may deepen further by late week according to some model output. Uncertainty remains regarding the expect track and intensity of this system at this time, but most guidance keeps the low pressure system south of 15N moving west through late week.

$$ Christensen