AXPZ20 KNHC 151605

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1605 UTC Sat Dec 15 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 1200 UTC surface analysis and satellite imagery through 1545 UTC.


Gulf of Tehuantepec Gale Warning: The tight pressure gradient over southeastern Mexico resulting from the combination of strong high pressure over northern Mexico and lower pressure south of Mexico is bringing strong gale force northerly winds over the Gulf of Tehuantepec. The observation from ship with call sign "VRJT8" indicated strong northeast gale force winds along with seas of 16 ft earlier this morning at 12Z when it was located near 14N96W. First visible satellite images clearly reveal an arc cloud line located about 450 nm SSW of the Gulf while propagating away from it. This feature marks the leading edge of the strong northerly surge, meaning that N to NE 30 to 45 kt gale force winds are already funneling through the Isthmus of Tehuantepec and across the Gulf. This strong gap wind event will continue through Sun night, before diminishing on Mon as the strong high pressure over Mexico shifts eastward and weakens. Seas of 12 to 18 ft with this event will subside to 9 to 13 ft Mon and to less than 8 ft on Tue as the northerly winds diminish to fresh speeds. Please refer to the latest high seas forecast issued under AWIPS/WMO headers HSFEP2/FZPN03 for more specific marine related details.


The monsoon trough axis extends from northwestern Colombia to 06N77W to 05N93W, where latest scatterometer data indicated that it transitions to the ITCZ and continues to 05N108W to 08N126W and to beyond 07N140W. Scattered moderate convection is noted within 60 nm south of the ITCZ between 126W and 129W.



The weak ridge over the area has diminished ahead of a weakening cold front that extends from near 32N130W to 25N140W. The lighter pressure gradient is maintaining light to gentle breezes across the area. Northwest swell with seas to 9 ft persist in the offshore waters of Baja California through the Revillagigedo Islands. The front will dissipate this afternoon before reaching the area, but associated northwest swell will reinforce the existing swell through Sun.

A second cold front will approach the region early next week. This will bring a new set of northwest swell, with seas in excess of 12 ft reaching the northern coast of Baja California Norte and Guadalupe Island by early Mon. Swell of 12 to 15 ft will cover the Baja offshore waters to the Revillagigedo Islands into mid week. Swell of this size and period will present hazardous seas for mariners, cause very powerful and dangerous surf along the Pacific reefs and beaches, and likely produce areas of modest coastal flooding and beach erosion.

Over the Gulf of California, strong high pressure north of region have been supporting moderate to fresh breezes across the basin. These winds will diminish through this afternoon as the high pressure weakens and shifts eastward.

A mid to upper-level disturbance approaching the area from the west may bring a few showers to the central and southern portions of the Baja California Peninsula and Gulf of California through Sun.


Gulf of Papagayo...Fresh to strong gap winds will pulse starting tonight and persist into early next week as high pressure builds north of the area. The gap winds will diminish late Tue night. Seas with these winds are expected to be 8 to 9 ft.Fresh winds will also pulse across the Gulf of Panama and Gulf of Fonseca tonight and Sun.

Elsewhere, gentle to moderate winds will persist on either side of the monsoon trough through early next week, as seas remain in the 4 to 6 ft range.


A mid to upper-level trough noted on water vapor imagery to be north of about 18N and between 115W and 134W is supporting scattered moderate convection within 60 nm of a line from 13.5N120W to 13N126W. The upper feature has also been supporting a surface trough, presently analyzed from near 14N130W to 09N139W. Scatterometer data from overnight last night indicated fresh to strong winds on the northern end of the surface from 17N to 19N between 121W and 128W. Concurrent altimeter data from early this morning showed seas to be as high as 12 ft in this area, due to the local winds and a component of longer period NW swell. NW swell in excess of 8 ft covers most of the area north of 06N and west of 115W.

Farther north, a weakening cold front extending from near 32N130W to 25N140W will dissipate this afternoon as it moves eastward. Models highly suggest that a second and stronger cold front will approach the northwest section of the area tonight, and move eastward across the waters north of 20N through early next week. The main impact will be a new round of NW swell, with combined seas in excess of of 12 ft to as high as 20 ft propagating across most of the region north of 12N and west of 120W Sun through late Mon.

During the early to middle part of next week, the leading edge of this next round of northwest swell will mix with shorter period northeast and east swell emerging from the gap wind areas, and possibly even southerly swell, to create an area of mixed seas south of 12N between 95W and 110W.

$$ Aguirre