000 AXPZ20 KNHC 120239 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 239 UTC Mon Mar 12 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 0000 UTC surface analysis and satellite imagery through 0230 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: Light to moderate onshore winds will prevail through early Mon morning. Strong high pressure ridging will build southward behind a strong cold front along the Sierra Madre Oriental of eastern Mexico and over the western Gulf of Mexico tonight through Mon night, then remain in place through Wed night. Winds will abruptly become northerly, then rapidly increase to fresh to strong over the Gulf of Tehuantepec by late Mon morning. Winds will continue to increase to gale force late Mon afternoon and peak around 45 kt Mon night into early Tue. Gale force winds will likely diminish by midday Thu, with brief lulls below gale force also possible during the afternoon hours Tue and Wed. Seas will peak in the 15 to 17 ft range Mon night or Tue morning. This latest gap wind event will finally wind down by Thu evening. Please see the latest Pacific Ocean High Seas Forecast product under AWIPS/WMO headers HSFEP2/FZPN03 KNHC, for more details. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A surface trough axis extends from 09N83W to 04N94W. The ITCZ axis continues from 04N94W to 04N110W to 02N120W to 07N140W. A second ITCZ axis is S of the equator and extends from just SW of the Galapagos Islands near 01S92W to 03S100W to 02S107W to 03.4S113W. Scattered moderate convection is within an area bounded by 05N108W to 02N108W to 01N116W to 02N118W to 04N117W to 05N113W to 05N108W, and also within an area bounded by 02S99W to 03.4S99W to 03.4S108W to 02S106W to 02S99W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the Special Features section for information on the Gulf of Tehuantepec developing gale warning. High pressure measuring 1019 mb is centered near 25N119.5W. The high ridges SE across the open waters W of the Baja California peninsula. The high will maintain 15 and 20 kt NW to N winds tonight through Tue. The high will weaken and dissipate by Wed as a decaying cold front approaches. Long period NW swell generated by winds behind the front will cause seas to build to between 6 and 8 ft W of 110W Wed through Thu, subsiding thereafter. Gulf of California: High pres just NW of the offshore zones is generating moderate to fresh NW winds over the central and southern Gulf, except from 24N to 27N where recent observations along both the coast of mainland Mexico and Baja California along the Gulf of California have been reporting fresh to strong northerly winds. The pressure gradient across the region will weaken Tue night through Fri, which will allow winds to diminish to between gentle and moderate. A cold front or remnant trough will approach Baja California Norte Fri night. Winds will become southerly in the northern Gulf of California and increase to fresh to near gale force. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... High pressure ridging over the Caribbean from the SW Atlc is weakening but is still causing moderate to fresh winds to pulse over the Gulf of Papagayo tonight through Tue. Winds over the Gulf of Papagayo will increase back to fresh to strong at night as the pressure gradient restrengthens in response to high pressure building SE over the Caribbean from the Gulf of Mexico Tue night through Fri night, peaking near 30 kt early Thu morning. Over the Gulf of Panama, gentle to moderate winds will prevail through Wed, increasing to moderate to fresh thereafter. Seas are expected to run between 4 and 6 ft as moderate cross-equatorial SW swell continue to arrive, building to 5 to 7 ft Thu and Fri as the winds increase. Elsewhere, expect gentle to moderate winds and 4 to 6 ft seas to prevail, except seas of 8 to 11 ft in northerly swells generated from a gale force gap wind event in the Gulf of Tehuantepec which will propagate into the Guatemala offshore waters Mon night through Tue night. REMAINDER OF THE AREA... A busy weather pattern remains in place across the NW and N central waters. A pair of remnant boundaries associated with old cold fronts extending from southern California to across the N central waters continue to dissipate. Associated winds are light to moderate at best with seas less than 8 ft. Meanwhile, the plume of tropical moisture heading NE from near the Hawaiian Islands has been diminishing in depth and extent, so the coverage of convection in this area has been decreasing. Even so, scattered moderate convection is within an area bounded by 30N129W to 30N118W to 27N120W to 21N131W to 22N140W to 24N130W to 30N129W. A stronger cold front is entering the NW corner of the discussion area, extending from 30N138W to 28.5N140W. An area of fresh to strong winds accompanies the front N of 27N. This area of winds will diminish and lift to the N of 30N by Mon night. Large NW swell will also accompany the boundary, reaching as high as 14 to 16 ft by Mon evening. The front will weaken as it moves across the waters N of 24N and W of 125W. A weaker cold front will introduce a round of reinforcing NW swell Wed night and Thu, with yet another decaying front dropping S for the end of the week with another set of NW-N swell. Mixed swell are generating an area of seas measuring close to 8 ft generally between 06N and 09N W of 128W. This area of seas will gradually propagate westward and eventually merge with a larger area of NW swell generated by the stronger cold front mentioned in the previous paragraph on Tue. $$ Lewitsky