NWS Guam wrote its last area forecast discussion before the first event at Jan 21, 7:55 AM UTC, 3 hours 5 minutes earlier.
Area forecast discussion, Jan 21, 7:55 AM UTC, 3 hours 5 minutes before
Area Forecast Discussion
National Weather Service Tiyan GU
555 PM ChST Tue Jan 21 2025
.Marianas Synopsis...
A broad, but weak trade-wind trough is moving away just west of the
Marianas. A few isolated showers and patches of cloudiness are left
in its wake, mainly near Saipan and Tinian. Elsewhere and upstream of
the Marianas, conditions are mostly clear and dry, with CIMSS MIMIC
Total Precipitable Water (TPW) values falling to 1.0 to 1.2 inches
just east of the islands. Surface observations and scatterometry show
moderate trade winds across the area.
&&
.Discussion...
Dry trades dominate across the region, occasionally interrupted by
weak, transient surface features which provide a boost in shower
coverage and cloud cover from time to time. Behind the latest
trough, conditions are dry with only 10 percent PoPs in the forecast
through Wednesday night. The subtropical ridge starts to reassert
itself north of the CNMI come Thursday, strengthening the pressure
gradient across the region and leading to an increase in trade winds
over the Marianas. A slight increase in showers can be expected with
the increase in trade-wind convergence, in addition to higher seas
and surf.
&&
.Marine...
Latest buoy data show combined seas of 4 to 7 feet near the
Marianas, while altimetry is peaking around 8 feet east of the
islands. Winds will remain gentle to moderate through Wednesday,
becoming moderate to fresh by Thursday. A pulse of increased trade
swell and north swell will arrive around this time, increasing seas
by a foot or two. This may also re-introduce a high risk of rip
currents for north and east facing reefs.
&&
.Eastern Micronesia...
The Inter-Tropical Convergence Zone (ITCZ) continues to develop
across eastern Micronesia and is now seen south of Pohnpei. Showers
have held back a bit longer than previously expected, remaining
south of Pohnpei and just south of Majuro. The forecast for Kosrae
remains relatively unchanged as showers have increased to scattered
there. For Pohnpei, delayed the onset of scattered showers until
Wednesday morning as the convection looks to slowly drift northward
overnight. For Majuro, the showers are seen just south of the
southern waters. These showers are slowly drifting north as well and
look to move into Majuro later this evening, no later than midnight.
For Kosrae, scattered showers are now in place over the island.
Models remain consistent keeping the ITCZ active for the next several
days at Pohnpei and Kosrae and through the end of the week for
Majuro. For the weekend, a drier trade-wind pattern looks to move
into the Marshalls, then slowly spread westward. Although model
guidance wants to keep the ITCZ active well into next week, it looks
more likely that the convergence will decrease with the ITCZ
dissipating over the weekend. This should allow the dry trade-wind
pattern to push into Kosrae and Pohnpei early next week.
Marine conditions remain the same, with fresh to strong trade winds
expected through Wednesday afternoon for Kosrae and Pohnpei, and
continuing through at least Friday at Majuro. Although altimetry
shows seas below 9 feet near Pohnpei and Kosrae, the Pohnpei buoy
showed seas peaking right at 10 feet today. Therefore, decided to
maintain the Small Craft Advisory (SCA) for both Pohnpei and Kosrae
through Wednesday afternoon. As the seas subside, surf is also
expected to fall below hazardous levels of 12 feet along east facing
reefs of Pohnpei, though the High Surf Advisory (HSA) will likely
need to be extended a bit longer for Kosrae as waves look to remain
above 8 feet. For Majuro, altimetry still shows seas up to 11 feet
east of the atoll. Model guidance indicates this will continue
through Friday night before dropping below 10 feet on Saturday. This
could also keep hazardous surf conditions going through Friday night.
&&
.Western Micronesia...
A broad trough ahead of the Intertropical Convergence Zone (ITCZ)
brought mostly cloudy skies and scattered showers to Chuuk today and
is slowly moving west, trending showers down to isolated late
evening. Breaks in a convergence zone to the south will keep showers
isolated to scattered over the next day or so, until ITCZ showers
gradually build northwestward into the region in the latter half of
the week. Models indicate a peak in showers Friday through Saturday,
before the ITCZ axis shifts back south early next week. In far
western Micronesia, a lull in activity near Palau and Yap is expected
tonight and Wednesday, then models indicate increased convergence to
the south from a possible disturbance near the equator or Near-
Equatorial Trough (NET) activity in the latter half of the week.
Being on the northern peripheries, Yap can expect isolated to
scattered showers whereas scattered showers across Palau are expected
late week and over the weekend.
Palau buoy shows seas between 4 to 5 feet and altimetry data
indicate seas between 6 to 8 feet farther east, composed of dominant
east swell. North swell is expected to diminish over the next few
days then another pulse of north swell, around 2 to 4 feet, is
expected to arrive late week and over the weekend to Palau and Yap.
This would only amount to 4 to 6 foot surf, so no advisories are
expected through early next week. Trade swell is expected to
increase another foot or two this week, with the highest seas near
Chuuk, reaching around 9 feet near midweek. This, and moderate to
fresh winds increasing to fresh, possibly strong by late week would
make seas choppy, nearing Small Craft Advisory conditions.
&&
.GUM WATCHES/WARNINGS/ADVISORIES...
GU...None.
MP...None.
Marianas Waters...None.
&&
Marianas: DeCou
East Micronesia: Kleeschulte
West Micronesia: Cruz