Tropical Weather Discussion

axpz20 knhc 222205

Tropical weather discussion
NWS National Hurricane Center Miami FL
2205 UTC sun Jul 22 2018

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 1800 UTC surface analysis and satellite imagery through
2145 UTC.

...Tropical waves...

A low-latitude tropical wave has its axis along 79w N of 01n, 
moving westward at about 15 kt. The wave is evident in tropical 
wave model diagnostics as well as a maximum in total precipitable
water satellite imagery. Scattered moderate isolated strong 
convection quickly developed this morning and continues east of 
the wave north of 07n to over much of Panama where the eastern 
segment of the monsoon trough is found.

A tropical wave has its axis along 92w/93w north of 04n to 
inland far southeastern Mexico, moving westward at 10-15 kt. The
wave is evident in 700 mb model guidance streamlines as well as 
a very pronounced maximum in total precipitable water satellite 
imagery. Numerous moderate to strong convection is occurring from
10n-13n between 94w-98w. Scattered moderate isolated strong 
convection is seen where the wave intersects the monsoon trough 
within 180 nm west of the wave from 06n-09n, and also within 60 
nm of 11n94.5w. Little development is expected of this wave over 
the next couple of days.

A tropical wave has its axis extending from 06n121w to newly 
formed low pressure near 10n123w 1010 mb and to 19n121w, moving 
westward 15-20 kt. The wave is associated with broad troughing 
at 700 mb as depicted in model guidance. Scattered moderate 
isolated strong convection is seen from 10n-14n east of the wave
to 116w, and also from 10n-13n west of the wave to 124w. 

...Intertropical convergence zone/monsoon trough... 

The monsoon trough axis extends from a 1010 mb low over
northwestern Colombia near 10n75w to 10n85w to 10n94w to
11n105w to 11n115w to weakening low pressure of 1009 mb at
13n140w. Aside from convection associated with the tropical 
waves, scattered moderate isolated strong convection is within 
240 nm south of the axis between 80w-89w, within 180 nm south of
the axis between 122w-129w, within 180 nm south of the axis 
between 133w and 136w, within 120 nm south of the axis between 
100w and 103w and within 60 nm of the axis between 107w-110w. 
Scattered moderate convection is within 180 nm south of the 
trough between 94w-99w.


Offshore waters within 250 nm of Mexico...

The southeastward extent of rather weak high pressure ridging 
that enters the region well beyond 250 nm of the Mexican coast 
is analyzed near the revillagigedo islands near 16n106w. The 
ridge is maintaining light to moderate NW winds across the 
Mexican offshore waters, except for the Gulf of Tehuantepec area 
as discussed below. Little change is expected in these conditions
during the next several days. A long period SW cross-equatorial 
swell is affecting the waters S of 15n. This extensive swell 
event will continue spreading northward, and will cause seas to 
build to the range of 7-9 ft in the open waters for all the 
forecast zones through Tue night.

Gulf of tehuantepec: the fresh to strong north winds indicated 
by the 1614z ascat pass will shrink in coverage this evening, 
but are expected to again pulse over through The Gap late
tonight through Mon morning before diminishing to light to
moderate early Mon afternoon and gentle S to SW winds Mon night 
and gentle variable winds Tue. Wind waves generated by the 
north winds are interacting with the SW swell event resulting 
in mixed seas south of the Gulf, with wave heights maxing out 
to 9 ft. These wave will slowly lower to 8 ft during Mon, then
subside slightly during Tue and into Wed.

Offshore waters within 250 nm of Central America, Colombia, and 
within 750 nm of Ecuador... 

Gulf of papagayo: fresh to strong easterly winds will pulse 
during the late night and morning hours through Wed morning 
before diminishing to fresh intensity. Seas from these NE to E 
winds will interact with the SW swell event to produce mixed seas
in the Gulf as high as high as 10 ft on Mon before seas begin to
slowly subside on Tue.

Northeast to east winds of only moderate speeds or weaker are 
forecast elsewhere N of the monsoon trough which will meander 
west of Central America between 07n-10n. Moderate to fresh S to 
SW winds are generally expected S of the trough axis during the 
next several days.

A long-period SW cross-equatorial swell event is already 
affecting the region as seas to the south of the Equator have 
build to 9 ft. Seas will peak between 8-10 ft on Mon in the open
waters, with the highest seas expected to the west of Ecuador.

Remainder of the area...   

A surface ridge extends east-southeastward from 32n140w to 
24n125w and to near the revillagigedo islands near 16n106w.
Weak low pressure of 1016 mb is analyzed at 32n129w, with 
a trough to near 25n130w. Widely scattered showers and isolated
thunderstorms are noted north of 30n and between 131w-135w. 
The low will move in a westerly motion through Tue while
weakening. It is expected to weaken to a trough from 32n139w to 
29n141w by Wed. The gradient between the ridge and lower 
pressure to its south in the sub-tropics and tropics is 
maintaining mainly moderate trade winds north of the monsoon 
trough south of 20n and west of 115w. Little change in this 
pattern is expected for the upcoming week. Swell producing
waveheights to a maximum of 8 ft generated by strong winds N of 
the area is propagating southward encompassing the discussion 
waters N of 29n between 130w-138w. This swell will continue to 
affect this region while slowly shifting westward and subsiding 
through Mon evening.

Newly formed low pressure of 1010 mb is along the tropical wave 
that extends from 06n121w to 19n121w. Fresh to strong winds are 
present within 60 nm of low in the E and se quadrants per the 
1756z ascat pass, with seas of 8-10 ft. Fresh winds are 
elsewhere within 120 nm over the E and se quadrants and within 
150 nm of the low remainder quadrants. The low is forecast to 
move in a west-northwest motion through the next 24 hours, then 
in west-northwest motion afterwards reaching to near 12n 132w by
early Wed afternoon. Fresh to strong winds are forecast from 
12n- 15n between 131w-134w, with seas of 8-10 ft by Wed.

A 1009 mb area of low pressure is centered at 13n140w, moving 
westward around 15 kt. Fresh to strong winds northeast to east 
are occurring from 14n to 17n west of 139w, with associated seas
in the range of 8 to 10 ft. Scattered moderate convection is 
seen within from 11.5n to 13n west of 136w. Scattered moderate 
isolated strong convection is present from 10n to 11.5n west of
136w. This low will shortly cross 140w, however, the gradient
between it and the high pressure to its north will be tight
enough to allow for fresh northeast to east winds from 14n-19n 
west of 138w through early Mon along with seas of 8-9 ft in mixed 
E and se swell. These swells will gradually decay by late Mon
night allowing for the seas to lower below 8 ft.

Large long-period SW swell is crossing the Equator, with seas of
8 to 10 ft extending from the southern hemisphere northward to a
line from 03.4s83w to 00n86w to 12n103w to 14n123w to 04n137w, 
as confirmed by satellite-derived sea height data received this 
afternoon. The swell will continue to propagate northward and 
allow for seas to build to 8 ft or above across most of the area
to the south of 25n and east of 133w on Mon. The swell will 
decay allowing for the seas to subside and seas subside Tue
through Wed.



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