969
FXPQ50 PGUM 172023
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
623 AM ChST Thu Jul 18 2024

.Marianas Update...
Model data has backed off a bit on rainfall amounts, but only a bit.
Looks like the peak will be Friday, so hit that day with numerous
showers as opposed to scattered for the rest of the week. The
Ritidian buoy briefly spiked to a height of 6 to 8 feet yesterday,
prompting the issuance of a high risk of rip currents. It has since
settled back down to between 4 and 6 feet this morning, so allowed
the high risk of rip currents to expire on schedule. The next week
is going to be fairly rainy, so as usual, Liberation Day is probably
going to be on the wet side for Guam...hopefully we can avoid a
total washout though.

&&

.Eastern Micronesia Update...
Kosrae remains under a high surf advisory through today. The ITCZ
remains the dominate feature of the region bringing locally heavy
showers to all 3 regions. Pohnpei and Kosrae look to be going into a
lull in the showers come tonight while Majuro will be later. Seas
just west of Majuro are staring to drop, last altimetry pass shows 7
to 8 feet. Winds are expected to diminish over the course of the
next 24 hours. The winds are expected to be gentle to fresh to start
the day off and by night become light to gentle. The strongest winds
are going to be near the heaviest of the showers.

&&

.Western Micronesia Update...
Overall little change in the forecast for Western Micronesia. Based
on satellite trends, trimmed the numerous showers for Palau and Yap
back to scattered. Reduced the winds a little at Chuuk, which ended
up lowering the wind waves, so the swells increased a little, and are
now at 4 to 6 feet through tonight.

Winds are expected to stay 15 knots or less, swells at Chuuk 4 to 6
feet today diminishing to between 3 and 4 feet for the weekend, and
swells at Palau and Yap being 3 to 4 feet the entire forecast period,
looks like more benign marine conditions are on tap, if you can deal
with the showers.

&&

.Prev discussion... /issued 543 PM ChST Wed Jul 17 2024/

Marianas Synopsis...
Very unsettled weather persists over Micronesia, and satellite shows
a large area of clouds and patchy showers approaching the Marianas
from the east and southeast. A gust front with 30 kt winds moved
across the islands at about 3PM, otherwise surface winds reported
from local airports have been east at 15 to 20 kt with occasional
stronger gusts. Ritidian buoy has been reporting combined seas of 6
to 7 feet with maximum waves up to the 9 to 12 foot range.

Discussion...
An area of surface troughing and patchy showers are arriving this
afternoon. Locally heavy rainfall is likely later tonight into
Thursday. Latest model guidance indicates a little less rainfall
than previously expected and shower coverage could trim back to
scattered by Friday through Saturday. Sunday weather is still
questionable at this time. It`s usually difficult to get fair weather
for the Annual Liberation Day. Changeable and unstable weather will
continue over the region. Models differ quite a bit in the details,
and as usual, the GFS is more aggressive than the ECMWF and
indicates that a developing disturbance will be just to the southwest
and west of Guam over the weekend. Also, GFS indicates a showery
weather pattern will likely develop by early next week.

Marine/Surf...
A surface trough approaching from east and southeast will cause
showers and isolated thunderstorms at times. Winds will be moderate
to fresh with gusts of 25 to 30 kt near showers. Combined sea of 5 to
8 feet will also be choppy as secondary swell arrives from southwest
to west during the next few days.

The risk of rip currents has become high along east facing reefs,
especially with the occasional bigger waves near the approaching
showers. Otherwise, there is a moderate risk along the east and north
facing reefs through Friday night. There is a low risk along south
and west facing reefs, unless a bigger than expected southwest swell
arrives. There will also be a moderate risk of lightning through the
next few days.

Hydrology...
The ESF/Hydrologic Outlook was re-issued for the heavy rain threat
for tonight through Friday. The trough approaching the Marianas will
cause numerous showers tonight and Thursday at least, and scattered
showers may linger into the weekend. Computer models differ in the
details quite a bit, and have generally backed off in the rainfall
amounts for the Marianas, while indicating that very heavy weather
could develop just southwest and west of Guam over the weekend.

Rainfall amounts of 2 to 4 inches are now expected for the local
forecast area tonight thru Friday, and showers could still linger
over the weekend. In the longer term, The GFS model in particular
indicates more showers for the Marianas next week.

Eastern Micronesia...
Active weather pattern across eastern Micronesia over the next few
days, with an ITCZ meandering and transitioning at times to more of
a zone of trade convergence. The convergence zone is enhanced to the
southwest of Pohnpei and Kosrae where it runs into the monsoon
trough. A surge in trade winds is also pushing into Majuro. Numerous
to occasional showers and isolated thunderstorms expected through at
least Thursday for Pohnpei, Kosrae and Majuro. Heavy downpours and
gusty winds expected. The convergence zone looks to fragment into a
series of troughs by the weekend. This pattern will still support
scattered showers and isolated thunderstorms across the region, but
showers will start to cluster more around troughs passing through the
convergence zone. The ITCZ could build back into the region from the
east next week, increasing shower and thunderstorm potential.

Gentle to moderate winds for Pohnpei and Kosrae, with moderate winds
and some fresh gusts to Majuro. Combined seas have lowered to 5 to 7
feet for Pohnpei and Kosrae and 6 to 8 feet for Majuro. Higher seas
and stronger winds will be possible with heavy showers and
thunderstorms through at least Thursday. The trade swell was high
enough to continue the High Surf Advisory for east reefs of Kosrae
through Thursday afternoon. As the trade surge weakens, seas look to
lower to 3 to 5 feet for Pohnpei and Kosrae and 4 to 6 feet for
Majuro, with winds becoming light to gentle for Pohnpei and Kosrae
and gentle to moderate for Majuro.

Western Micronesia...
Scatterometry data shows the monsoon trough entering the region
around 10N to a disturbance near Yap Proper and continues east-
southeast across eastern Yap State and Chuuk State. Over the past
several days, short-lived vorticity features have been embedded in
the trough, leading to localized areas of more intense showers and
coverage. Today, satellite and model trends do show a loose
circulation near Yap, but models does not suggest much development
with this particular feature. With the gradual north to northwest
shift in the monsoon trough, westerly flow can finally extend to Yap
tomorrow, while still supplying showery monsoon weather in far
western Micronesia over the next few days. Models show showers
decreasing over the weekend and early next week for Yap and Palau, as
the trough pushes farther to the north. For Chuuk, there will be a
shift in light to gentle west winds, becoming variable overnight as a
trade disturbance moves into the area tonight. Then, a fragmented
ITCZ pattern is expected for the remainder of the week through early
next week, maintaining periods of showery weather.

Altimetry and scatterometry data show seas of 3 to 5 feet and light
to moderate winds. Palau`s buoy shows seas slightly less than 3 feet
since it is sheltered from the westerly swell. Localized effects of
heavier showers will still lead to choppy seas at times across Palau
and Yap over the next few days, and for Chuuk tonight with a passing
disturbance. Southwest to west winds and swell in far western
Micronesia will keep seas between 3 and 5 feet, while seas near Chuuk
look to stay between 4 and 6 feet.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...None.

MP...None.

Marianas Waters...None.
&&

$$

Marianas: Stanko
Micronesia: Bowsher