109
FXPQ50 PGUM 150726
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
526 PM ChST Sat Jun 15 2024

.Marianas Synopsis...
Partly cloudy to mostly cloudy skies are seen across the Marianas
this afternoon, with isolated showers. Scattered showers are seen
just east and south of the islands. Gentle to moderate trade winds
with strong gusts prevail. Ritidian buoy shows seas between 5 and 6
feet while altimetry shows 4 to 6 feet over the waters, with 5 to 7
feet to the east.

&&

.Discussion...
Shower coverage is much less than was previously expected due to the
trough that was expected to bring the increased convection to the
islands weakened significantly. Although isolated showers are what is
seen across the Marianas now, another impulse is approaching from the
east with scattered showers east and south of the Marianas. Therefore,
maintained scattered showers for tonight as this feature approaches.
The upper-level low is now northwest of the Marianas, resulting in
less favorable conditions for the development of thunderstorms over
the region. Regardless, there is still a risk of thunderstorms, so
decided to keep a slight chance of thunderstorms for tonight. A dry
pattern will then return to the Marianas. This dry pattern will
continue through next week for the CNMI, however, another round of
scattered showers is expected for Guam Monday and Monday night as a
weak disturbance moves through to the south of Guam coastal waters,
bringing scattered showers to Guam. By Tuesday, the dry pattern will
return to Guam and continue through next week.

&&

.Marine...
A slight chance of thunderstorms will continue across the Marianas
waters through tonight as a weak trough moves through. Otherwise,
mostly gentle to moderate trade winds are expected over the next
several days. Combined seas look to increase overnight tonight as a
building trade swell moves into the region. Seas are expected to
build from 4 to 6 feet to between 5 and 7 feet by Sunday morning.
Seas will then begin to subside Sunday night, dropping to between 3
and 5 feet by the middle of next week.

&&

.Eastern Micronesia and Chuuk...
As mentioned in the last discussion, the ITCZ has fragmented and now
a series of troughs and weak convergence dominates the weather
pattern. A trough near Chuuk has pulled away faster than expected, so
showers are isolated across Chuuk, but as the weak trade convergence
generating scattered showers near Pohnpei pushes westward, expect
showers to become isolated at Pohnpei overnight and through tomorrow
while increasing at Chuuk after midnight. Kept thunderstorms out of
the forecast for Pohnpei through Sunday and through the middle of
next week for Chuuk due to the lack of any significant surface
features and upper-level support. Over by Kosrae and Majuro, a more
notable trough and trade-wind convergence is generating scattered
showers and isolated thunderstorms near Kosrae, extending through
the Marshall Islands. A TUTT low has also entered the region from
across the Date Line and is north of the Marshalls. As the trough and
convergence drifts westward, expect scattered showers to continue at
both Kosrae and Majuro through the weekend, while the potential for
thunderstorms will decrease at Majuro Sunday, but increase at Kosrae
Sunday night and Monday as the TUTT moves west-northwest towards
Wake Island. Given the fragmented nature of the convection across the
region, there probably will be times when showers become isolated,
but the exact timing is hard to pinpoint given the variability
between the different models. Also, by the middle of next week, the
GFS and ECMWF suggest the ITCZ will try to rebuild in the central
Pacific and then push into eastern Micronesia once again. If this
occurs then showers will once again spread across the region from the
Marshall Islands to Chuuk State.

Combined seas are expected to be 3 to 5 feet across most of the
region and up to 6 feet at Majuro over the next several days.
Scatterometry data shows gentle to moderate winds across the region,
with moderate to fresh winds associated with the area of convection
near Kosrae and extending back towards the Marshall Islands.

&&

.Western Micronesia for Palau and Yap...
The surface trough that extends into the region from the Philippines
now passes south of Palau and towards the equator near 146E, based on
the curvature of winds in scatterometer data. Most of the scattered
showers and isolated thunderstorms is also along and south of the
trough axis, leaving Yap Proper and Palau with some cloud cover, but
isolated showers this evening. Yap is expected to remain isolated
through the night and into Sunday morning, before a trade-wind trough
moving through Chuuk State and into eastern Yap State starts to push
into Yap Proper Sunday afternoon. For Palau, models show the surface
trough lifting northward slightly overnight, increasing showers
after midnight. Showers will then retreat back south Sunday and
allow showers to become isolated again, before the trade-wind trough
mentioned earlier moves through Palau Sunday night and into Monday.
Through the next several days, limited the mention of thunderstorms
in the forecast to when more notable features such as the trade-wind
trough moves through as upper-level support has weakened. Looking
beyond Monday, the surface trough will linger in far western
Micronesia as the monsoon pattern expected during the summer tries
to establish itself across southeast Asia, while light to gentle
trade-winds continue to push back into Yap and Palau at times. This
transitional period will trend towards being a wet pattern for Palau
and Yap, but periods of isolated showers are expected, it`s just
difficult to pinpoint when these periods will occur.

Buoy and altimetry data show seas around 2 to 3 feet, and
scatterometry data indicates light to gentle winds. Marine conditions
are not expected to change that much over the next several days,
except for a slight increase in trade swell that would bump seas up
to 4 feet around Yap Monday.

&&

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

$$

Marianas: Kleeschulte
Micronesia: Schank