000 AXPZ20 KNHC 050924 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 614 UTC Tue Dec 5 2017 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 0900 UTC. ...SPECIAL FEATURES... Gulf of California: Strong high pressure is currently building from the U.S. Great Basin and northern Rockies southward towards the desert SW of the U.S., and has begun to support the development of fresh to strong NW flow in the far northern Gulf N of 29N. Winds will increase to minimal gales later morning in the northern Gulf as the pressure gradient continues to tighten, then will diminish below gale by this evening as it slackens slightly. Meanwhile, the fresh to strong winds will spill southward across the entire Gulf by mid-week. Another area of strong high pressure will build across the region Wed night through Thu and is expected to initiate another round of gales across N and N central portions Thu. Seas are expected to build up to 9 ft across the northern part of the basin by late today and to 6 to 9 ft across the remainder of the basin Wed through Thu. Also, as the strong winds develop across the Gulf, strong northeasterly gap winds will bleed through gaps in the mountain peaks across the northern peninsula and spill across the Bay of San Sebastian. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from low pressure near 07N78W to 10N86W to 07N90W, then transitions to the intertropical convergence zone and continues westward to 18N125W to 08N140W. Scattered moderate to isolated strong from 09N to 15N between 125W and 135W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec: Local overnight drainage effects are allowing moderate to fresh gap winds early this morning. These winds will diminish by late morning, but will pulse again to 20 kt tonight. Winds will increase to fresh to strong late Wed ahead of a cold front moving across the western Gulf of Mexico, arriving in southern Mexico Thu. Winds will further increase to minimal gales by Thu night as the cold and dry air pushes into the Gulf of Tehuatepec. Seas will build to 15 ft by early Fri, with seas 8 ft or greater reaching as far as 500 nm downstream to the W-SW of the Gulf of Tehuantepec. Looking ahead, strong high pressure building behind the front over central Mexico will support a persistent strong gale event across the Gulf of Tehuantepec through late in the week. Elsewhere off the Pacific coast of Mexico, weak high pressure is maintaining gentle to moderate breezes across the region. Long period NW swell to 9 ft is noted beyond 120 nm off Baja California in recent altimeter satellite passes. This swell will subside below 8 ft through late today. High pressure building north of area will result in strong gap winds pushing across low lying areas of Baja California Norte and into adjacent waters Thu. A larger plume of strong NE winds will push off the coast of Baja California Sur north of Cabo San Lazaro Thu night and Fri, with seas 8 to 10 ft reaching beyond 250 nm offshore. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Fresh NE winds across the Papagayo region this will pulse to strong tonight with seas downstream building to 6 to 8 ft. Winds and seas will diminish through late week as strong trades winds over the southwest Caribbean diminish and veer SE. Looking ahead, strong high pressure will build N of the region, allowing strong gap winds and building seas to reappear by Sun. Winds may even approach minimal gale force late Sun night through early Mon. Elsewhere, light to gentle N to NE winds are expected N of the monsoon trough, and mainly moderate S to SW winds are expected to the S of the monsoon trough. Seas are in the 5 to 7 ft range in SW swell this evening to the S of the monsoon trough, and will subside to 4 to 6 ft through mid week. REMAINDER OF THE AREA... An upper level short wave trough extending soutward along 138W north of 27N is lifting north of the area. This has been supporting a 1012 mb complex surface low near 26N135W. A recent scatterometer pass indicated 20 to 30 kt easterly winds between 25N and 30N between 130W and 140W, between the complex low pressure area and high pressure north of the area. Divergence aloft on the right rear entrance area of an upper jet maximum south of the upper trough is supporting an area of showers and thunderstorms from 09N to 15N between 125W and 135W. Residual fresh to strong SE to S winds will persist through late Wed north of 27N between 130W and 140W as the upper support lifts north, and ahead of a cold front approaching the area from the northwest. Scattered showers and a few thunderstorms will persist in this area as well. The front will stall and dissipate just northwest of the discussion area early Fri. Looking ahead, strong southerly flow will return Sat north of 28N and west of 135W ahead of yet another cold front approaching from the NW. Elsewhere Scattered moderate convection is noted A surface trough embedded in the tradewind belt extends from near 09.5N126W to 17N118W, and is racing near 20 kt along the ITCZ. Strong trad winds just ahead and behind the trough continue to initiate scattered moderate isolated strong convection from 07.5N to 16N between 115W and the trough, and is being enhanced by upper level divergence. The trough will move W and gradually become absorbed in a deep layered low pressure area along 132W by Wed night. A sharp and deep layered trough is moving very slowly into W portions of the area, where a pair of low pressure centers and a stalled front have developed at the surface. Recent analysis suggests a 1011 mb low pressure center near 27N138W with a trough extending to a second 1011 mb low near 24.5N136W then a stationary front to 22N135.5W to beyond 19N140W. Strong E to SE winds N of 21-22N between these surface features and 126W are initiating scattered moderate convection, while scattered moderate to strong convection is occurring from 08.5N TO 22N, W of 125W. Upper level divergence E of the upper level trough there is sustaining the convection across this area and will maintain unstable conditions there into early Wednesday. The pressure gradient between a strong ridge across the NE pacific and the two low centers is supporting these strong winds E of the lows and fronts to about 129W. The lows will lift N and drag a new front into the area from the W by Wednesday afternoon to produce persistent strong SE to S winds across NW portions. Seas will remain at 8-11 ft in NW swell, or higher, during this time. Elsewhere, NW swell greater than 8 ft covers almost the entire discussion waters beyond 250 nm offshore of Central and South America. These seas will gradually decay through the early part of the week. $$ Christensen