436
FXPQ50 PGUM 091940
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
540 AM ChST Sat May 10 2025

.Marianas Update...
Satellite observations show a partly cloudy skies and isolated
showers across the Marianas. The main change with this forecast
package was to reduce dewpoints to better match the trend from the
last few days with drier relative humidity values in the afternoon.
The ECMWF has been performing the best with dewpoints the last few
days so did a heavy blend with a slight mix of the GFS and CMC
ensembles.

No changes were made to the marine forecast. Combined seas of 4 to 6
feet are expected to continue through this weekend before an east-
northeast swell allows for seas to rise a foot or so.

&&

.Fire Weather...
The Red Flag Warning has been extended until Sunday afternoon. A
trace of rain fell at the Guam International Airport yesterday. The
KBDI rose to 727, which is in the extreme category due to daytime
winds of 15 to 20 mph. Terrain forcing of winds and occasional gust
could make fire fighting drastically harder. The fire danger is
expected to become critical during the daytime hours, with afternoon
relative humidities expected to drop below 60 percent, and elevated
winds, especially in higher terrain. A wetting rain is not expected
for at least the next several days, and the KBDI is expected to
continue to rise.

&&

.Eastern Micronesia Update...
Not much change was made this forecast update, as the going forecast
has things well in hand. One thing that we`ll be keeping an eye on
though is the developing convection east of Kosrae. If this trend of
rapid cloud top cooling and increasing areal size continues,
rainfall potential may need to be ramped up (increased). The question
remains is this just part of the nocturnal "flare up". We`re betting
that it is so will keep the forecast as it is right now, but time
will tell if an update is needed.

&&

.Western Micronesia Update...
Here too the changes were minimal this update. The main item of
interest is at Palau, where a "ribbon" of drier air will pass over
the region, briefly dropping PWATs (Precipitable Water Values) down
to 1.3 inches today, before rapid moistening to near 2.3 inches
occurs by later tonight. Thus, rainfall potential increases
noticeably tonight, when scattered showers may once again develop.

&&

.Prev discussion... /issued 631 PM ChST Fri May 9 2025/

Marianas Synopsis...
A Red Flag Warning remain in effect through at least Saturday
afternoon. Satellite imagery shows isolated showers. Ritidian buoy
shows combined seas of about 4 feet.

Discussion...
The Marianas remains deeply entrenched in a dry trade-wind regime,
although some moisture may be on the way. Time heights suggest a
slight deepening of the the moisture layer for the beginning of next
week. The GFS model date (our most aggressive model) suggests a
possible increase in showers also for the beginning of next week,
however the ECMWF is lagging behind. For these reasons Probability of
Precipitation (PoPs) were increased to high-end isolated instead of
scattered. Regardless of if these showers come to pass, the dry
trade-wind pattern is expected to remain.

Marine...
Combined seas are around 4 to 6 feet and could increase 1 foot
around Monday. Winds are expected to be moderate through next week.
A moderate risk of rip currents along east facing reefs is expected
to remain for the next few days. So overall, benign conditions are
expected to continue.

Fire weather...
About 0.01 inches of rain has fallen at the Guam International
Airport so far today. The KBDI remains at 724, which is in the
extreme category due to daytime winds of 15 to 20 mph. Terrain
forcing of winds and occasional gusts could make fire fighting
drastically harder. The fire danger is expected to become critical
during the daytime hours, with afternoon relative humidities expected
to drop below 60 percent, and elevated winds, especially in higher
terrain. A wetting rain is not expected for at least the next several
days, and the KBDI is expected to continue to rise.

Eastern Micronesia...
A weakening and shifting convergence zone will allow the patchy
showers near Pohnpei and Kosrae to further diminish over the next few
days, joining Majuro in a drier trade-wind regime. Winds are expected
to increase over the weekend, with breezy conditions expected by
early next week at all three forecast points.

Combined seas of 4 to 6 feet near Pohnpei and Kosrae, are expected to
increase a foot or two next week as trade swell and wind waves
strengthen. Combined seas of 6 to 8 feet near Majuro will remain as
such for much of the forecast period, with brief dips expected through
the middle of next week.

Western Micronesia...
A near-equatorial trough (NET) is generating moderate convection in
the far southern portion of Palau and moderate to deep convection
across open waters in southern Yap State and southern Chuuk State,
closer to a couple of weak, embedded circulations (near 1N143E and
1N153E). North of the NET, a broad trade-wind trough that brought a
brief period of thunderstorms to Palau earlier this morning, has
weakened and moved farther west of the islands. Model guidance
suggested scattered showers lingering in southwestwern waters later
this evening, however not seeing much support based on satellite
trends, so only expecting isolated showers tonight for Palau. Another
trough moving through eastern Yap State is expected to bring a
period of scattered showers to Yap Proper late tonight and Saturday,
arriving to Palau Saturday night. The convergence zone near Chuuk has
weakened a bit throughout today, although scattered showers and
isolated thunderstorms are still expected over the next several days
with brief lulls in showers possible. Next week, model guidance
continues to show some gradual development with the NET, leading to
increased convergence and showers across Yap and Palau.

Combined seas of 3 to 5 feet near Yap and Palau, and 4 to 6 feet
near Chuuk will continue over the next several days. Overall, winds
will be gentle to moderate, increasing to moderate to fresh near
Chuuk around the middle of next week.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...Red Flag Warning until 4 PM ChST Sunday for GUZ001.

MP...None.
Marianas Waters...None.
&&

$$

Marianas Update: Williams
East/West Micronesia Update: Doll
Marianas: Bowsher
East Micronesia: Montvila
West Micronesia: Cruz