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Tropical weather discussion
NWS National Hurricane Center Miami FL
1005 UTC Thu Jun 20 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
meteorological analysis.
Based on 0600 UTC surface analysis and satellite imagery through
0945 UTC.
...Intertropical convergence zone/monsoon trough...
monsoon trough axis from 10n85w to 11n100w to 1008 mb low pres
near 11n110w to 09n128w where it transitions to the ITCZ to
09n140w. Scattered moderate to strong convection exists within
120 nm S of the axis between 92w-97w. Scattered
moderate/isolated strong convection is within 120 nm S of the
axis between 115w-126w...and also within 60 nm of the axis
between 107w-115w.
...Discussion...
Water vapor imagery shows an upper trough now having shifted to
the far NE part of the area. In its wake...W to NW flow upper
flow is present N of 27n and W to near 135w/136w where mid to
upper ridging is evident. This ridging extends se to an upper
anticyclone at 18n134w. The upper flow becomes swly W of 136w
ahead of an ewd advancing upper trough W of the area. Another
upper anticyclone is seen near 21n123w. Both of the anticyclone
are joined by a ridge that extends ENE to over srn Baja
California...and to SW of the area at 15n140w. Associated
anticyclonic flow covers the area from 13n to 27n. With this
anticyclonic flow in place...resultant moderate to strong
subsidence is keeping dry and very stable atmospheric conditions
throughout this portion of the area as noted by the mostly clear
skies present there. Broken high clouds are seen streaming ewd
into the NW corner of the area across the ridge described above
as the upper trough W of the area taps the deep tropical central
Pacific region. These high clouds reach to near 130w before they
evaporate in the moderate to strong air aloft.
An upper trough extends from an upper cyclone centered near
16n112w to 15n100w. This is supporting a 1008 mb surface low
embedded within the monsoon trough at 11n108w. E of the low...the
latest available ascat passes indicated a surge of moderate to
fresh SW flow into the monsoon trough...and providing further
fuel to convection associated with the monsoon trough. To the se
and S of the upper low at 16n112w...mid/upper level ridging is
present. A small upper level low is seen over the Gulf of
Tehuantepec. The low is providing a favorable environment for
deep layer atmospheric moisture to exist over the far ern part
of the area as the upper flow pattern becomes diffluent there.
Scattered strong convection in clusters is seen within 30 nm of
13n90w. Scattered moderate/isolated strong convection is
elsewhere within 90 nm of the coast of Central America from 09n
to 14n. This convection should linger into the next 24-48 hrs
with times on between where it will weaken then redevelop.
Over the next 48 hrs...the nwp models are in reasonable
agreement that the low near 11n110w will drift slowly W.
Meanwhile...a second surface low is expected to form near
12n100w through Sat per model guidance...and eventually interact
with the low near 11n110w beyond 48 hrs. Both of these features
will be embedded within a broad area of low pres expected to
materialized over the ern portion of the area through the next
few days.
Elsewhere at the surface...a nearly stationary 1028 mb high pres
center is analyzed just NW of the forecast waters at 33n140w
with a ridge extending sewd to near 21n121w. The pres gradient
to its E in combination with lower pres over the wrn U.S. W
coast is allowing for mainly fresh to strong winds near the
coast of California with a portion of these winds to gale force
from 30n to 36n between 120w-123w. NW to N swells generated by
these winds are spreading S into the NE portion of the area to N
of 22n between 118w and 124w where NW-N winds of 20-25 kt and
seas of 9-10 ft are present in as noted in the 0438 UTC ascat
pass from this morning. These winds are forecast to lower to 20
kt or less in 24 hrs with seas to 9 ft in NW to N swell N of 26n
between 118w and 124w in 48 hrs. By 48 hrs...this area of swells
will be confined to N of 28n between 118w-122w. A weak surface
trough is suggested by partial ascat data and in the low cloud
motion to be located from near 11n134w to 09n135w. The ascat
data indicated NE 20 kt winds W of the trough. Seas there are
8 ft in a NE swell. The nwp models suggest that the trough will
translate ewd through late Fri night where it should extend from
11n137w to 09n138w. At that time the gradient to its W should
allow for NE winds of 20-25 kt with seas to 9 ft.
$$
Aguirre
