759
FXPQ50 PGUM 191836
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
436 AM ChST Sun Apr 20 2025

.Marianas Update...
Satellite and radar show partly cloudy skies and isolated showers for
this morning within the Marianas Waters. The buoys reveal combined
seas of 4 to 6 feet, trending toward 3 to 5 feet already.

Satellite shows a new trade-wind disturbance coming in, either late
this afternoon or early this evening. Introduced scattered showers
for tonight based on this. Otherwise the forecast was in good shape,
and while many grids were refreshed, the changes were mainly
cosmetic.

The KBDI has risen to 648, however it appears that winds will be
below critical fire weather thresholds for the next several days.
Marine conditions are benign and will become even more so over the
next couple of days, then remain that way for at least a few
additional days.

&&

.Eastern Micronesia Update...
Kosrae:
The biggest change was to significantly ramp up POPs (Probability of
Precipitation) at Kosrae to 90 percent (categorical coverage), while
mentioning locally heavy rainfall. A lead tropical MCS has developed
south of Kosrae, with another currently developing east of Kosrae.
Both have had a decent amount of lightning in them with cloud top
temperatures colder than -80 deg. C. This is typically "a lock" for
getting heavy rainfall, especially considering the slow-moving nature
of them. As a result, lowered both afternoon and overnight
maximum/minimum temperatures.

Majuro:
Satellite imagery and streamline analysis shows a subtle trough to
your east, where showers are trying to percolate. Confidence is a
little uncertain in this though, at least for this afternoon.
Conversely, a "slug" of moisture will be moving into the region later
today into tonight, helping to destabilize the atmosphere more, so
it`s even possible rainfall potential may need to be increased for
tonight.

Pohnpei:
The main change here was to add isolated thunderstorms to the
forecast tonight, as you`ll be on the "fringe" (edge) of a deeper
moisture plume bypassing you to the south. However, moisture does
increase some and even the ECMWF convective parameters are marginally
supportive of thunderstorms. Thus the inclusion into the forecast.

&&

.Western Micronesia Update...
Palau:
The main change here was to increase POPs (rainfall potential) as a
disorganized cluster of multicellular convection continues to fire
(develop) to your southeast. This is being driven by a subtle surface
trough to your east that`ll approach this afternoon, moving overhead
tonight. Was tempted to go with likely wording for tonight, but
it`ll be close if the "better action" misses you just to the south.
will defer to the day shift to monitor this possibility.

Yap:
Another little subtle trough is to your east, and the better moisture
is to your south. The question is will daytime heating be sufficient
to destabilize the atmosphere sufficiently for low-end scattered
shower coverage. Given a more active pattern compared to weeks past,
opted to be optimistic and carry the scattered shower wording, as any
additional convergence from the approaching trough (if it holds
together) may just be enough "goods for the sauce" to get things
going. Otherwise, look for a typical trade pattern to continue with
hit-and-miss showers from time to time.

Chuuk:
You`re looking fairly limited in terms of rainfall potential, and
clouds based on the fastest satellite imagery. The better moisture
and lift is displaced well southwest and southeast of you, offering
little more than isolated/brief showers in the offering through
tonight.

&&

.Prev discussion... /issued 351 PM ChST Sat Apr 19 2025/

Marianas Synopsis...
Moderate trade winds with occasional fresh gusts prevail across the
region this afternoon. Visible satellite imagery shows patchy clouds
and showers over Tinian and Saipan, and partly cloudy skies over
Guam and Rota. Buoy data indicates combined seas have decreased to 4
to 6 feet.

Discussion...
Weak convergence ahead of a trade-wind trough is generating a line
of patchy clouds and showers over Tinian and Saipan this afternoon.
Model guidance shows a slight boost in showers around midnight, so
have added low-end scattered showers (30 percent chance) to tonight`s
forecast for Tinian and Saipan. Otherwise, a fairly quiet weather
pattern remains in store for the region for the remainder of the
weekend and this upcoming week.

Marine/Surf...
Combined seas of 4 to 6 feet continue to diminish this weekend as
trade winds and swell subside, falling to between 3 and 5 feet this
upcoming week. Gentle to moderate trades become light to gentle
starting Sunday night. A moderate risk of rip currents is expected to
continue along east facing reefs through the weekend and along north
facing reefs through Sunday.

Fire weather...
As of this afternoon, no rain has fallen at the Guam International
Airport today. The chance of a wetting rain today is unlikely, which
would allow the KBDI to rise from 643, currently in the high category
for fire danger. Abnormally dry conditions continue, which would
bring afternoon relative humidities near 60 percent. Even so, winds
are expected to be gentle to moderate and Red Flag conditions are not
expected to be met over the next few days.

Eastern Micronesia...
A long band of trade-wind convergence stretches east-northeastward
from western Micronesia south of all forecast points. For Majuro and
Kosrae, a couple of weak trade-wind troughs are interacting with the
convergence to enhance convection and drag the convergence a little
farther north. This will result in increased showers and isolated
thunderstorms developing and moving into both Majuro and Kosrae
later this evening. There is a much lower chance of thunderstorms for
Majuro, however, due to weak upper-level convergence under a weak
high pressure ridge. Latest satellite shows convection increasing to
the east of Kosrae with lower level showers seen to the east of
Majuro. Over the next several days, it appears likely that the band
of convergence will continue to drift north and expand, resulting in
convection spreading farther north as well. This pattern looks to
spread westward into Pohnpei early next week. For Pohnpei tonight
into the weekend, it looks to remain fairly dry, with only isolated
light showers through Sunday afternoon. There is a trade-wind trough
evident to the south of Pohnpei, however, any convection associated
with this trough will remain south of Pohnpei coastal waters. The
remainder of next week is more questionable as to whether the band of
convergence remains as active as the models predict. Due to the
uncertainty of this, decided to maintain POPs (Probability of
Precipitation) at around 40 percent through the end of the week for
Kosrae and Pohnpei. Majuro will see a drier pattern return a bit
earlier though, with POPs dropping to around 20 percent around the
middle of next week.

Marine conditions look to remain benign, with seas of 5 to 7 feet
continuing to slowly subside, reaching 3 to 5 feet by Monday at
Pohnpei and Kosrae and 4 to 6 feet for Majuro. Gentle to moderate
trade winds will prevail through next week.

Western Micronesia...
The proximity to a nearby convergence zone and developing NET will
keep patchy showers near and over Palau through the weekend into next
week. Meanwhile, a minor trough upstream is expected to bring a
slight uptick in showers to Yap Sunday and Sunday night, followed by
further drying thereafter. A similar pattern is expected over Chuuk
through the weekend into early next week, followed by an ITCZ-like
pattern developing that may bring on-and-off showers in the second
half of next week.

Combined seas of 5 to 6 feet are expected to fall another foot or two
across the region by the middle of next week.

&&

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

$$

Marianas Update: Stanko
East/West Micronesia Update: Doll
Marianas: Cruz
East Micronesia: Kleeschulte
West Micronesia: Montvila