386
FXPQ50 PGUM 140822
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
622 PM ChST Tue May 14 2024

.Marianas Synopsis...
Satellite imagery showing partly cloudy skies and spotty trade
showers for the CNMI, with mostly cloudy skies and scattered showers
over Guam. Latest altimetry data is indicating seas of 4 to 7 feet
for the coastal waters.

&&

.Discussion...
A surface trough will pass to the south of the Marianas through
early Wednesday. Enough moisture and convergence along the northern
periphery of the trough, as shown by the CIMSS MIMIC Layer Pwat, may
creep far enough north to impact Guam. Introduced low-end scattered
showers and mostly cloudy skies for Guam tonight, while the CNMI
should see spotty showers and partly cloudy skies. Beginning
tomorrow through the weekend, expect generally partly cloudy skies
with isolated trade showers over the coming days. May see a slight
uptick in clouds and showers at times, as wrinkles in the trades pass
through the region. Some model guidance is suggesting a potential
tropical cyclone developing between Yap and Chuuk and drifting
towards the Marianas early next week.

&&

.Marine/Surf...
Trade winds will generally be moderate with some fresh gusts through
Friday, then increase and become moderate to fresh over the weekend
as the gradient tightens between high pressure passing to the north
and a tropical disturbance to the south. Combined seas of 4 to 7
feet through Saturday. Seas look to increase through the weekend into
early next week as an elevated swell emanating from a storm system
north of Hawaii arrives and wind waves increase.

There will be a moderate risk of rip currents along east facing
reefs through Friday, while the rip current risk will remain low
along all other reefs. Surf may build slightly for east and north
facing reefs over the weekend, possibly increasing the rip current
risk to high for east reefs and moderate for north reefs.

&&

.Tropical Systems...
An increasing number of deterministic and ensemble guidance is
showing a tropical disturbance developing and possibly becoming a
tropical cyclone (TC) over eastern Yap State or western Chuuk state
by this weekend. The overall model and ensemble trend is for a
disturbance or TC to develop and pass somewhere in the vicinity of
western Micronesia and the Marianas through early next week. While
uncertainty in the forecast is high, continue to monitor upcoming
forecasts for updates on the potential development, track and
strength of the potential TC, especially those across the Republic
of Palau, Yap State, Chuuk State and the Marianas.

&&

.Eastern Micronesia...
An Inter-Tropical Convergence Zone (ITCZ) is now seen lying across
eastern Micronesia, with scattered showers associated with the ITCZ
seen across Pohnpei and Kosrae, with numerous showers across the
Marshalls near Majuro. Latest model guidance is in disagreement over
what is expected across the region beyond Thursday, with the GFS
trying to develop a TC over western Micronesia, changing the flow
pattern across eastern Micronesia. The GFS, however, is the outlier,
with the other models, including the GFS Ensemble, showing the
pattern remaining as is for most of the week. Based on the extreme
difference in the GFS from the other models, chose to use a blend of
all models except the GFS. This would keep an overall wet pattern
across eastern Micronesia into next week. For the short term,
(through Wednesday), all models support numerous showers remaining
across Majuro, with the strongest convergence along the ITCZ. Later
in the week, the southeasterly flow into the ITCZ looks to weaken and
turn more easterly, allowing POPs (Probability of Precipitation) to
drop to around 30 percent by Friday. Meanwhile, POPs of 30 to 40
percent look to be the rule for Kosrae, while Pohnpei could see as
high as 50 percent Thursday and Thursday night.

Moderate to fresh trade winds at Pohnpei are expected to subside,
becoming gentle to moderate by Thursday evening. Gentle to moderate
trade winds will continue at Majuro through the weekend. Kosrae will
see the lightest winds, with gentle to moderate winds becoming light
to gentle by the end of the week. Combined seas of 5 to 7 feet are
expected over the next several days.

&&

.Western Micronesia...
The main feature affecting western Micronesia continues to be the
Near-Equatorial Trough (NET) that is seen on the latest surface
analysis and satellite data to the south of Palau, Yap and Chuuk. The
NET extends eastward from near 3N130E to a circulation centered near
2N143E, then continues southeast to end at the equator near 153E. A
band of very strong convergence is seen north of the trough and
circulation, near Weno, with numerous showers to the west that are
approaching the island. Expect numerous showers to move into Weno
overnight as this band of convergence drifts over the area. It
appears likely that the trough will remain active, with the strong
convergence remaining near or over Chuuk though at least Wednesday
night. Latest model guidance varies dramatically on the forecast near
the end of the week, with the GFS showing a strong circulation
developing and moving toward Weno over the weekend, with other models
showing little more than a few weak circulations popping up along
the NET, with some of the models moving the NET close enough to
increase convection over Yap and Palau. Therefore, the forecast for
western Micronesia has very low confidence after Friday. Based on
model performance over the past several days, will keep the forecast
close to previous forecasts. Decided to maintain an overall wet
pattern across Chuuk, with POPs of 40 to 50 percent through the
beginning of next week. For Yap and Palau, maintained POPs around 20
percent. However, if the NET does push far enough north, Palau and
Yap could see POPs in the 30 to 40 percent range. We will continue to
monitor western Micronesia for any indicators that this pattern will
change.

Without developing a strong circulation like the GFS is doing, winds
look to be gentle to moderate through the week for Yap and Chuuk and
light to gentle for Palau. Combined seas look to remain between 3
and 5 feet at Palau and 4 to 6 feet for Yap and Chuuk.

&&

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

&&

$$

Marianas: Slagle
Tropical: Slagle
Micronesia: Kleeschulte