070
FXPQ50 PGUM 210839
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
639 PM ChST Tue May 21 2024

.Marianas Synopsis...
Afternoon satellite imagery shows fair weather across the Marianas
with a few trade-wind showers passing through bringing short-lived
showers and brief gusts to around 30 mph. Both the 00Z RAOB and MIMIC
TPW indicated about 2in of precipitable water near Guam, with MIMIC
TPW showing drier conditions over the CNMI. The higher TPW over Guam
is connected to the increased moisture field extending northward from
the West Micronesia circulation, Invest 93W. 93W remains broad and
weak, centered south of Yap near 5N138E. Seas of about 6-8 feet are
found around the Marianas with highest seas to the east of the
islands.

&&

.Discussion...
Made a few short-term forecast changes, mainly to reduce showers for
Guam and remove the thunderstorms for the short term since deeper
moisture had not pushed as far north into the area as models had
previously shown. Had considered a slight chance of thunderstorms
for the Guam area into Wednesday, but despite the near 2in TPW, the
mid and upper atmosphere remain quite dry. NUCAPS profiles from the
afternoon METOP-B/C passes show very shallow moisture in the region
between Guam and Chuuk with much drier conditions aloft, as noted in
Himawari low and mid-level water vapor imagery. Model data shows the
moist layer limited to around 700mb then significant drying aloft.
Later in the week, though, around Thursday into Friday, deeper
moisture will push through the Guam area and is expected to bring an
uptick in showers for Guam and Rota as well as a small chance for
thunderstorms. Trade winds will hold steady through the week before
decreasing over the weekend with next week seeing gentle easterly
winds.

&&

.Marine...
A high risk of rip currents will continue through Wednesday afternoon
with 6-8 ft seas resulting in surf along east facing reefs up to 9
ft. Trade winds and swell will begin to subside late week and into
the weekend with seas eventually falling to the 4-5 ft range by
Sunday.

&&

.Tropical systems...
The broad and weak circulation, 93W, south of Yap near 5N138E remains
the tropical feature of interest. It is currently rated as a LOW for
development potential by the JTWC, meaning TC development is unlikely
within the next 24 hours. Afternoon visible satellite imagery shows
an exposed low-level circulation center with deep convection
displaced to the east. West of the center, clusters of showers and
thunderstorms are developing amid a swath of drier air feeding in
from the west, as noted in recent MIMIC TPW imagery. Deterministic
and ensemble model guidance largely keeps 93W as a broad circulation
with a large center of weak winds as it potentially passes near Palau
Wednesday or Thursday. The most likely effects from 93W to the Palau
and Yap areas will be the heavier shower and stronger easterly wind
gust potential as 93W heads WNW. Areas south of 93W`s center will
experience much lighter winds out of the west. Once 93W heads into
the PI Sea, models show a slow organization of the circulation with
GFS still being more aggressive in the 5-10 day time frame, as has
been the case for quite some time.

&&

.Eastern Micronesia...
Shallow cumulus clouds are seen across the three forecast points and
for most of the region. Isolated showers are expected for Pohnpei
tonight, there are some residual clouds and showers seen nearby with
the cold front to the northeast. This is expected to move out of
Pohnpei`s waters by tomorrow. Expect a slightly drier pattern for
Kosrae and Pohnpei for a day or two then showers increasing by the
week`s end as a TUTT and upper low enter the region, most likely
being on and off scattered showers for Kosrae and Pohnpei. Beginning
of next week, a moderate ITCZ pattern develops, bringing scattered
showers again, and possibly locally heavy showers as the models
indicate pockets of deeper convection.

Gentle to moderate trade winds and trade-wind swell continues across
the region. An afternoon altimetry pass near Kosrae indicates
combined seas around 5 to 6 feet and the Majuro buoy recently
reported seas around 5 feet.

&&

.Western Micronesia...
A broad circulation, Invest 93W, was located south of Yap and
southeast of Palau, near 5N138E. Convergence along the northern
peripheries is bringing widespread showers and isolated thunderstorms
to most of Yap State. An upper-level trough to the northwest, helped
maintain clusters of thunderstorms around Ulithi today. As this
upper-level feature moves west and weakens overnight, it will
gradually decouple from surface features, losing out on that
supplementary support for thunderstorms. Although, 93W, alone, will
undoubtedly supply a busy weather pattern for far western
Micronesia. Currently, the favored trajectory of this circulation is
to pass just south of the main islands of Palau late Wednesday
night, then continuing northwest into the Philippine Sea. Although
models show little development until it is well to the northwest of
the region, periods of heavy rainfall and gusty winds are still
possible Wed-Thu for Yap and Wed night-Thu for Palau. As 93W
continues its departure from the region, a trade-wind pattern looks
to return next week. Farther east, Chuuk is outside the grip of 93W
and a relatively quiet pattern is expected. Subtle troughing in the
trade flow will bring periodic upticks in clouds and showers, then
next week an ITCZ pattern begins to build back in from eastern
Micronesia.

Winds will be mainly moderate for Yap and Chuuk and gentle to
moderate for Palau through the week. Fresh to strong gusts are
possible near heavier showers for Yap and Palau Wed-Thu, due to the
passage of 93W. Seas are 4 to 6 feet and up to 7 feet at Chuuk and
are expected to subside a foot or two over the weekend as trade swell
weakens.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...High Rip Current Risk through Wednesday afternoon for GUZ001.

MP...High Rip Current Risk through Wednesday afternoon for MPZ001>003.

Marianas Waters...None.
&&

$$

Marianas: Aydlett
Tropical: Aydlett
Micronesia: Hong/Cruz