417
FXPQ50 PGUM 140820
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
620 PM ChST Fri Jun 14 2024

.Marianas Synopsis...
Partly cloudy to mostly cloudy skies are seen across the islands,
with scattered showers moving in from the east. Gentle to moderate
trade winds prevail. Ritidian buoy shows seas around 4 feet while
altimetry shows seas of 4 to 7 feet east of the waters.

&&

.Discussion...
A modest trade-wind trough is evident on satellite and ASCAT analysis
to the east of the Marianas. Along with the trough, A TUTT cell is
seen to the northeast of the islands. The TUTT cell is providing
upper-level divergence across the region. As the trough to the
east moves closer to the islands, the divergence is expected to
increase convection over the Marianas. Satellite and Global Lightning
Detection (GLD) show numerous showers with embedded thunderstorms
east of the Marianas coastal waters. Showers are slowly increasing
now, with scattered showers likely to be over the area through the
evening. Near midnight, the showers and thunderstorms ahead of the
trough will move into the area, bringing numerous showers and
isolated thunderstorms to the islands. The trough and TUTT cell are
expected to drift slowly westward, maintaining a wetter pattern over
the islands through Saturday night. Numerous showers and isolated
thunderstorms are expected to continue through the day Saturday,
decreasing to scattered during the afternoon. As the features move
through the Marianas, they will also increase the potential for gusty
winds with the heavier showers and thunderstorms, with gusts to 30
mph possible. By Sunday, a drier pattern looks to return to the
region. This dry pattern looks to be short lived, however, for Guam
and Rota as a weak circulation is expected to push through just south
of Guam, bringing another round of increased convection to Guam and
Rota Monday through Tuesday. By Tuesday evening, the dry pattern is
expected to return to Guam and Rota and continue through Friday.
Meanwhile, Tinian and Saipan look to remain dry Sunday through the
end of next week.

&&

.Marine...
Other than the showers and thunderstorms expected over the next few
days, not much going on in the marine environment. Gentle to moderate
trade winds will prevail across the Marianas through most of next
week. However, occasional strong gusts are possible tonight through
Saturday afternoon with heavier showers and thunderstorms. Combined
seas of 4 to 6 feet will build slightly to between 5 and 7 feet over
the weekend. This is expected increase the rip current risk along
north facing reefs to moderate for a short time. Seas will then
subside a bit beginning early next week.

&&

.Eastern Micronesia and Chuuk...
The Inter-Tropical Convergence Zone (ITCZ) continues to extend across
from the Marshall Islands to Pohnpei State, but it has pulled back
from Chuuk State. Also at Chuuk, trade-wind flow is fairly diffuse
and unsupportive of showers and thunderstorms, but weak convergence
is expected to rebuild at Chuuk later tonight bringing scattered
showers back to Chuuk after midnight. Otherwise, scattered to
numerous showers and isolated thunderstorms extend along the ITCZ and
is affecting all the primary forecast points from Majuro to Pohnpei.
Some occasional gusty winds up to 25 to 30 mph over land and 25 to
30 knots over the waters are in the forecast for Kosrae and Pohnpei
with the heavier showers and thunderstorms. The ITCZ will shift north
and south through the weekend, while a trough is expected to break
off from the ITCZ and move into Chuuk Saturday night increasing
showers to numerous. By Monday, the ITCZ is expected to fragment into
a series of troughs, keeping periods of scattered showers and
isolated thunderstorms through most of next week.

Altimetry shows combined seas across the region are around 4 to 6
feet, though seas will be locally higher near showers and
thunderstorms. Scatterometer data shows winds are gentle to moderate
along the ITCZ with pockets of fresh winds embedded within the
heavier convection, with strong gusts possible, especially around
Kosrae and Pohnpei. The trade swell subsides slightly this weekend,
decreasing seas by a foot, and then rebuilds early next week.

&&

.Western Micronesia...
Satellite imagery shows scattered showers and isolated thunderstorms
across Yap Proper and Palau this evening. Winds are also light and
variable at Palau and Yap as a weak surface trough extends from the
Phillipines towards Palau and then merges with the weak trade-wind
troughs in eastern Yap State. This surface trough is potentially a
developing weak monsoon trough, as it struggles to extend back
towards southeast Asia ,and is an early indication of a transition
to the monsoonal pattern that occurs during the summer. The surface
trough is expected to linger in far western Micronesia while models
show the trade-winds trying to push back over Yap and Palau late this
weekend. This transitional period to the monsoonal pattern will
continue to support low-end scattered showers across Palau and Yap
over the next several days. The TUTT cell near the Marianas is
starting to move through the northern islands of the Marianas this
evening. The TUTT is slightly further north than expected, but kept
isolated thunderstorms in the forecast through Saturday night to
highlight the potential for thunderstorms south of the TUTT, but
fairly confident the risk of thunderstorms from the TUTT will
diminish Sunday and Monday. Around Monday night and Tuesday, a
trough that is expected to break off from the ITCZ will move out of
Chuuk State and into Yap State and then Palau. As this trough moves
through it will increase the potential for thunderstorms once again
for Monday night and Tuesday.

The buoys near Palau and Yap and altimetry data show seas are around
2 to 3 feet. Winds will remain light around Palau through at least
the weekend, but easterly winds are expected to become light to
gentle at Yap around Saturday.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...None.
MP...None.
Marianas Waters...None.
&&

$$

Marianas: Kleeschulte
Micronesia: Schank