140
FXPQ50 PGUM 231918
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
518 AM ChST Sun Nov 24 2024

.Marianas Update...
Minor edits to the forecast this morning. The dry trade-wind regime
continues today with spotty showers. Have sped up the passage of a
trade-wind trough, with scattered showers beginning later tonight
and continuing through Monday night. Increased mid to upper-level
moisture and upper-level support look to bring potential for
isolated thunderstorms. Beginning Wednesday, a surface trough and
higher moisture will drift north through the Marianas and bring an
increased potential for showers and thunderstorms through the end of
the work week.

Marine conditions will approach but look to stay just below Small
Craft Advisory criteria over the coming days. Combined seas of 6 to
8 feet will gradually rise to 7 to 9 feet by Monday as the trade
swell increases and longer period northerly swells pass through.
Winds will be moderate to fresh through at least midweek, with some
strong gusts possible at times. A moderate risk of rip currents today
along north, east and south facing reefs today. The rip risk will
become high along east reefs and moderate along west reefs by late
tonight.

&&

.Fire Weather...
Guam airport received only 0.04 inches of rain yesterday and the
KBDI rose to 262, which is still in the low category but approaching
the moderate category. A wetting rain is unlikely today but a couple
of chances will occur next week beginning Monday.

&&

.Eastern Micronesia Update...
Minor changes were made to the forecast. Decreased shower coverage at
Pohnpei and Kosrae through tonight, as the trade-wind convective
surges surrounding the islands and their waters have started to
weaken considerably earlier. Majuro`s forecast remains largely
unchanged, with a slight decrease in shower coverage today, but the
trade-wind surge is expected to remain just outside the northern
coastal waters for much of today. In addition, the marine forecast
remains largely unchanged at Pohnpei, Kosrae, and Majuro.

&&

.Western Micronesia Update...
Upped the shower coverage slightly at Palau due to the proximity of
cluster of thunderstorms to the northeast moving in along with a
trade-wind trough, meanwhile showers are expected to remain largely
on-and-off at Chuuk today. Yap`s weather forecast and the marine
forecast for Palau, Yap and Majuro remain unchanged.

&&

.Prev discussion... /issued 459 PM ChST Sat Nov 23 2024/

Marianas Synopsis...
Himawari visible satellite shows spotty, light showers across the
region, some pushed along by very weak, short-lived outflow
boundaries. Skies are partly cloudy across the islands, and surface
observations show moderate to fresh easterly flow, with occasional
gusts up to around 25 mph. Recent buoy data near Guam and Saipan
show combined seas of around 4 to 6 feet. Nearby altimetry shows 5
to 7 foot seas, east and west of the Marianas.

Discussion...
A dry trade regime continues across the Marianas. Wind speeds have
increased over the last day or so, and scatterometry data shows the
moderate trade-wind surge now extends further west of the Marianas
over portions of western Micronesia. Recent observations at Yap and
Palau show moderate to fresh trades, along with a few gusts exceeding
20 mph. Drier conditions will continue for the remainder of the
weekend, the only showers in the area a result of localized trade-
wind convergence. On Monday, a weak trough riding along the northern
periphery of the Intertropical Convergence Zone (ITCZ) will cross the
area, slightly increasing shower chances for the start of the
workweek. On Wednesday, a remnant ITCZ fragment looks to lift
northwest across the islands as a stronger surface trough, increasing
the potential for some locally heavy showers and associated strong
wind gusts for the latter half of the week. Models have pulled back
slightly on trade wind speeds, but the expected pattern remains the
same. Winds will remain fairly steady for the remainder of the
weekend, with a possible slight increase Monday through Wednesday as
the subtropical ridge strengths north of the Marianas. The ECMWF
continues to run roughly 2-4 knots higher than the GFS for the first
half of the week.

Marine...
Combined seas of around 5 to 7 feet will gradually rise to 7 to 9
feet by Monday as the moderate trade surge continues, and trade
swells see an increase. Winds will remain moderate to fresh with
occasional gusts in the low 20s, possibly increasing a few knots for
the first half of the week. Elevated trade winds will contribute to
higher, choppier seas, which could be hazardous to small craft at
times this coming week. The chance of showers and thunderstorms over
coastal waters increases during the middle of next week onward.

Eastern Micronesia...
A very active Inter-Tropical Convergence Zone (ITCZ) runs across the
region from southern Chuuk State northeastward over southern Pohnpei
State and Kosrae, then eastward over the central Marshall Islands to
beyond the Date Line. Heavy showers and a few thunderstorms continue
to develop in large areas over Eastern Micronesia and that inclement
trend will continue for the couple of days while the ITCZ drifts a
little farther west and west-northwest. Models are hinting at drier
conditions as the ITCZ diminishes, but multiple trade troughs along
with trade-wind convergence will maintain an elevated chance of
showers into next week.

Elevated winds and seas will continue into next week. Combined seas
could rise to 6 to 9 feet for Pohnpei and Majuro, and 5 to 8 feet
for Kosrae, comprised of a higher trade swell and longer period
northerly swells. Winds will be moderate to fresh with some strong
gusts near heavier showers and thunderstorms.

Western Micronesia...
The active ITCZ pattern in eastern Micronesia is pushing into Chuuk
this evening, with visible satellite imagery showing showers and
thunderstorms producing outflow boundaries that are moving at around
25 kt (~30mph). This has led to gusts of 25 kt added to the coastal
forecast for tonight, with breezy conditions around 25 mph for the
island forecast of Chuuk. Further west, a weak trade-wind trough near
Yap is producing scattered showers and isolated thunderstorms from
Yap Proper and across Ulithi, Sorol, Woleai, and other nearby
islands. Most of Palau is experiencing partly cloudy skies and
isolated showers, but as the trough near Yap moves north of Palau
tonight and Sunday, scattered showers and isolated will move into
Palau after midnight.

As the ITCZ continues westward, a wetter pattern is expected across
the region for the first half of the upcoming week. Right now models
favor most of the showers will be along and south of 8N, which would
favor slightly less rainfall over Yap Proper when compared to Palau
and Chuuk, especially for Sunday when the trough at Yap Proper moves
off to the west and the ITCZ starts to push into Palau, passing just
south of Yap Proper. A moderate trade-wind surge, mainly between 10N
to 20N, will continue through the first half of the week keeping
winds moderate to fresh across the region. The ITCZ will start to
fragment and become ill-defined by the middle of the upcoming week,
reducing the overall potential for showers and thunderstorms, but
passing trade-wind troughs will still bring periods of scattered
showers to the region. As the trade-wind surge weakens later in the
week, winds will also start to come down slightly.

Moderate to fresh trade winds with some strong gusts will be
possible, especially near heavier showers and thunderstorms. Seas
will rise over the next few days as multiple elevated northerly
swells pass through the region and the east-northeast trade flow
increases due to the ongoing moderate trade-wind surge. Seas will
peak around 5 to 7 feet for Chuuk around Sunday and Monday and for
Palau around Monday and Tuesday. Yap waters could feel more impacts
from the swells and slightly stronger trade winds, with seas possibly
rising to 7 to 9 around Monday or Tuesday. Models continue to keep
marine conditions just below hazardous levels for small craft with
seas below 10 feet and winds below 22 kt. Any increase in winds or
seas could trigger the issuance of a small craft advisory if it looks
like conditions warrant such advisory. After Tuesday, models have
winds and seas diminishing slightly as the trade-wind surge weakens.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...High Rip Current Risk from this evening through late Monday night
     for GUZ001.

MP...High Rip Current Risk from this evening through late Monday night
     for MPZ001>003.

Marianas Waters...None.

&&

$$

Marianas Update: Slagle
Micronesia Update: Montvila