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Tropical weather discussion
NWS National Hurricane Center Miami FL
0405 UTC Sat may 18 2013
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 0000 UTC surface analysis and satellite imagery through
...Intertropical convergence zone/monsoon trough...
The monsoon trough axis extends from 07n78w to 10n86w to 05n102w
to 07n107w...then resumes from 10n118w to 1008 mb low pres near
07n125w to 06n133w. The ITCZ axis extends from 06n133w to
05n140w. Scattered moderate to strong convection is within 120
nm S of the monsoon trough between 92w and 94w...from 06n to 11n
between 114w and 120w...and also from 10n to 13n between 120w
and 123w. Scattered moderate convection is within 90 nm in the
NE semicircle of the low...and also within 120 nm S of the
monsoon trough between 130w and 133w.
Aloft...an upper anticyclone is centered over 28n135w. An upper
trough stretches from far northern Baja California through
22n120w to 20n137w. Water vapor satellite imagery indicates mid
to upper level moisture present across the waters behind the
trough axis and under the upper anticyclone. A jet stream branch
with speeds of 50 to 70 knots is along 15n W of 120w...then
turns NE to across northern Mexico. Deep tropical moisture is
being advected from along the ITCZ and monsoon trough to the NE
across central Mexico within 600-720 nm ahead of the upper
trough. Elsewhere aloft...easterly winds are present over the se
portion of the area with additional tropical moisture being
advected to the W along the monsoon trough.
At the surface...1026 mb high pres is just W of the discussion
waters near 32n141w with a ridge extending se through 30n132w to
21n109w. Anticyclonic flow covers the waters N of 16n W of 115w
with gentle to moderate NE-E winds and 5-7 ft seas...except in
the W central waters W of a line from 19n140w to 15n133w to
10n140w where fresh trades are present along with 8-9 ft seas
commingling in NE wind waves and long period SW swell. These
winds and seas will diminish and subside by late Sat night as
the pres gradient relaxes over the area.
The 1007 mb remnants of Alvin are centered near 12n114w.
Scattered moderate convection is within 180 nm W of a line from
20n106w to 06n112w. Earlier visible satellite imagery continued
to show an exposed center as the region remains under upper
level westerly shear...with the center continuing to move to the
W...while any deep convection remains at least 75 nm E of the
center. Fresh to strong winds are within 180 nm in the NE
semicircle of the remnant center...along with 8 to 12 ft seas in
a broad mix of swell. The remnant center is forecast to move to
12.5n117w Sat evening...then to 13n120w sun evening.
Long period cross-equatorial mainly SW swells will continue to
propagate well into the central portion of the area through Sun
afternoon...mixing with shorter period confused seas generated
by the circulation of Alvin.
Fresh to near gale force northerly winds will set up along the
California coast this weekend as high pres builds W of the
region along with troughing over interior California. These
winds will generate NW swell which will cover the waters N of
29n between 118w and 123w by Sun afternoon.