AXPZ20 KNHC 291633
Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1605 UTC Tue Sep 29 2020
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
Based on 1200 UTC surface analysis and satellite imagery through
Tropical Depression Eighteen-E is centered near 13.3N 108.5W at
1500 UTC moving W at 9 kt. Estimated minimum central pressure is
1005 mb. Maximum sustained wind speed is 30 kt with gusts to 40
kt. Scattered moderate to strong convection is noted from 10N to
20N between 103W and 116W. The system is forecast to steadily
intensify as it moves on a westward to west-northwestward track
during the next several days. The current forecast has the
depression becoming a tropical storm this evening just outside of
the offshore waters near 13.8N 110.4W, then continuing WNW, and
reaching hurricane intensity Wednesday evening. Please read the
latest NHC Public Advisory at
https://www.nhc.noaa.gov/text/MIATCPEP3.shtml and Forecast/
Advisory at https://www.nhc.noaa.gov/text/MIATCMEP3.shtml for
Gulf of Tehuantepec gale warning: A strong gale force gap wind
event is expected across the Gulf of Tehuantepec late today
through Fri night as cold front moves across the Gulf of Mexico.
The pressure gradient between high pressure building behind the
front and the eastern Pacific monsoon trough will tighten over
the area. This will increase winds funneling through the Chivela
Pass into the Gulf of Tehuantepec. Winds will rapidly increase
to gale force by late this afternoon, reaching 30-40 kt by
tonight. At that time, seas will build to 15-18 ft. Swell
generated from this event are forecast to reach 100W on Wed.
Please read the latest NWS High Seas Forecast issued by the
National Hurricane Center at website
www.nhc.noaa.gov/text/MIAHSFEP@.shtml for more details.
Of note, the 20-year climatology of the Tehuantepec gap wind
events indicates that on average 16 gale-force events and 5
storm force-events occur in the Gulf of Tehuantepec each cold
season. Most gale-force events occurred during November and
December, while most storm-force winds occurred in January.
Based on latest model trends and the present evolving synoptic
scale setup, this forecast event most likely will supersede the
previously recorded earliest start date of October 3rd.
...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...
The monsoon trough extends from 10N74W to 10N84W to T.D.
EIGHTEEN-E NEAR 13.3N108.5W to 09N140W. Scattered moderate
isolated strong convection is noted from 03N to 11N between 78W
and 96W and within 120 nm S of trough between 127W and 140W.
OFFSHORE WATERS WITHIN 250 NM OF MEXICO...
Please see above for more on the Gulf of Tehuantepec gale force
gap wind event.
Elsewhere, a weak ridge west of Baja California will maintain
gentle to moderate NW to N winds across the region for the next
few days. Gentle to moderate northerly winds will prevail across
the northern Gulf of California through tonight while mainly
light to gentle winds are expected elsewhere across the Gulf most
of the forecast period. Elsewhere, light to gentle winds are
generally expected across the waters from Las Tres Marias Islands
to Puerto Angel for the next several days. T.D. Eighteen-E is
expected to become a large hurricane. The size of the system will
generate a large area of seas greater than 8 ft spreading from
swell out and away the cyclone center. This south swell will
spread across the offshore waters west of the Baja California
peninsula Thu into the weekend.
OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, and
WITHIN 750 NM OF ECUADOR...
Moderate southerly flow prevails S of the monsoon trough, with
gentle winds north of the monsoon trough. Combined seas are
currently 5 to 7 ft in a mix of wind waves and southerly swell.
Long period SW swell is moving over the waters between Ecuador
and the Galapagos Islands, with seas to 8 ft. These seas will
subside below 8 ft tonight. Seas generated by the gap wind event
in the Tehuantepec region will propagate across the offshore
waters of Guatemala and El Salvador beginning on Wed morning.
REMAINDER OF THE AREA...
Please see Special Features section above for newly developed
Outside of T.D. Eighteen-E, a weak pressure gradient prevails
with light to gentle winds prevailing N of the monsoon trough,
and gentle to moderate winds S of the monsoon trough. The cross
equatorial swell across the waters S of 15N has started to
subside, with seas in the 6-8 ft range. These seas will continue
to subside trough the middle of the week. New NW swell will
propagate into the NW waters the middle of the week. Seas will
build to 9 ft over the far NW waters by Wed night. T.D.
Eighteen-E is expected to become a large hurricane. The size of
the system will generate a large area of seas greater than 8 ft
spreading well away from the cyclone center. By Saturday, seas
greater than 8 ft will cover much of the waters N of 10N and W of