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Tropical weather discussion
NWS National Hurricane Center Miami FL
1605 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 1200 UTC surface analysis and satellite imagery through
...Intertropical convergence zone/monsoon trough...
the remnants of Alvin are embedded in the monsoon trough axis
near 12n116w. Numerous moderate to strong convection was between
60 nm and 180 nm of its E quadrant. Scattered moderate with
isolated strong convection was elsewhere from 07n to 16n between
111w and 118w.
The monsoon trough axis extends from 09n78w to 10n89w to 06n102w
to the remnants of Alvin to 10n120w to 09n123w. The ITCZ axis
extends from 09n123w to 08n131w to 04n140w. Scattered moderate
to strong convection was within 90 nm S of the axis between 86w
and Costa Rica. Scattered moderate with isolated strong
convection was within 45 nm N and 150 nm S of the axis between
93w and 103w. Scattered moderate convection was within 60 nm N
of the axis between 120w and 123w and within 180 nm N of the
axis between 123w and 128w.
the 1007 mb remnants of Alvin are centered near 12n116w. This
low pressure system fell between scatterometer passes this
morning and did not see an altimeter swath near the center.
Winds to 30 kt are believed to lie primarily E of the
center...with winds greater than 20 kt spanning the area within
210 nm NE semicircle and se quadrant. Seas are believed to be as
high as 11 ft under these conditions...with cross-equatorial
southwesterly swell keeping seas above 8 ft over a large area S
of the low between 100w and 126w...primarily S of 05n. The low
is expected to continue on a westward track at about 10 kt over
the next few days as it gradually weakens. 20-25 kt winds will
shift to the N semicircle by Mon as the low moves from the se
side of the subtropical high to S of the high.
The 1025 mb subtropical high was analyzed near 35n137w with a
ridge extending se through 32n120w to 30n125w to 15n107w. A
moderate NW breeze continues E of the ridge axis along the coast
of Baja California N of 26n according to the 0420 UTC ascat-a
pass. Winds are expected to increase off the California coast
sun and Mon as a cold front...currently impinging on the
subtropical high from the N...sweeps through the offshore waters
there. The subtropical high is expected to shift N of the front
sun and ridging will strengthen over N forecast waters. NW swell
will travel S of 32n beginning early sun and expand to waters N
of 27n between 118w-128w by Mon morning.
Moderate to fresh trade winds were observed by subsequent
ascat passes and a windsat pass from 0246 UTC in the area N of
the ITCZ to about 20n. Seas to 9 ft were observed by earlier
altimeter passes generally in the area from 06n-21n W of 127w.
Winds will remain below advisory criteria here through the
forecast period and seas generated by trade wind flow will shift
W of the area by sun...but seas from the remnants of Alvin will
quickly move into the area late sun into Mon.
An area of scattered moderate to strong convection along the
coast of Costa Rica is noted in the section above. This
convection is being enhanced by supper level divergence between
20 kt easterlies to the S and 5-10 kt southeasterly winds to the
N. Meanwhile...an area of upper diffluence between southeasterly
winds on the SW side of an anticyclone near Acapulco Mexico and
a ridge axis along 03s between 90w-110w is enhancing convection
along ITCZ between 93w-103w. This area coincides with the
highest precipitable water values outside of the remnants of
Alvin within the forecast area. Flow aloft here should continue
to support an increased chance of convection through the end of
the forecast period Mon morning.