Drought in Guam, December 1 to 31, 2021

Area Forecast Discussion
National Weather Service Tiyan GU
729 PM ChST Tue Nov 30 2021

.Marianas Synopsis...
Moderate southeasterlies prevail in the Marianas, as a surface trough
extending from Tropical Storm Nyatoh brings scattered showers and
isolated thunderstorms tonight. Ipan buoy indicates seas between 6
and 7 feet.

&&

.Discussion...
Unstable atmospheric conditions induced by the main trough overhead
and a secondary trough right after, will keep the Marianas under
wetter conditions and cloudier skies through Wednesday night. After,
the region will be situated in a surface ridge and an upper-level
high that will keep precipitation to a minimum through early next
week. By next week Wednesday, model guidance indicates a potential
for a tropical disturbance that may bring increasing showers. Due to
it being an extended period forecast, there is great uncertainty to
the event happening and as such, will be monitored for potential
development.

&&

.Marine...
While the Ipan buoy shows seas well below the forecast, the most
recent altimetry pass supported by the nearshore wave models
indicate seas around 8 feet further into the eastern coastal waters,
peaking close to 9 feet just northeast of Saipan. As such, the seas
are below Small Craft Advisory criteria so the advisory was cancelled
a few hours earlier, but seas are still considered elevated with a
possibility for occasional gusts of 25 knots near heavier showers.
Due to the incoming east-northeast swell generated by an expansive
cold front to the north, the risk for rip currents will remain high
through at least late Wednesday night for east facing reefs. Model
guidance indicates that the rip risk will become moderate once the
northeast secondary swell weakens and then gets replaced by a
northwest swell sometime Friday evening. In addition, improving
conditions warranted a cancellation of the High Surf Advisory for
surf dropping below advisory criteria. Still, the surf on east facing
reefs should stay elevated for at least the next few days.

&&

.Hydrology...
So far today, WFO Guam's official rain gauge has measured
approximately 1 inch of rainfall since midnight, with the total
rainfall over the last 2 days almost 3 inches. USGS rain gauges
around Guam have measured between 1.5 and 2.5 inches in the last 24
hours, which corresponds with the previous projection for today.
Lastly, the USGS rainfall totals for the last 2 days fall between 3
and 5 inches, falling within previous projections as well.

&&

.Tropical systems...
Tropical Storm Nyatoh (27W) continues to intensify as it tracks
slowly west. Morning ASCAT-B showed mostly 30 kts, but there were a
few 35 kt wind observations as well. Heavier showers and
thunderstorms are seen on the eastern and southern side, also where
the winds are converging.

&&

.Eastern Micronesia...
Scattered showers tonight for Majuro and then scattered showers for
Kosrae and Pohnpei tomorrow as the ITCZ pushes through. At Majuro,
scattered showers will probably extend into Thursday due to a
surface trough developing over the area. Also the models show the
ITCZ weakening around this time.

Expect a high surf advisory for Kosrae's north and east facing reefs
this weekend. Next Monday we'll see advisory conditions for small
craft and high surf for Majuro. On Thursday, an upper low spins off
east of Wake island, then tracks south towards Majuro. Still about a
week out, but it looks like there is a possibility for inundation for
Majuro.

&&

.Western Micronesia...
For Yap, we're expecting to see some showers tonight as 27W moves
away from Yap. Some smaller feeder bands are developing and may
bring increased rainfall later tonight, but still expecting rain
amounts to be low. Wednesday night, we'll see increased shower
activity and gusts along a convergence zone when 27W is further
north.

For Koror, we saw some steady southwest winds today, and recent
satellite imagery showed minor feeder bands beginning to develop
overhead. We're still expecting isolated showers for tonight as the
heavier weather and converging winds are further east and should
pass through Koror around Thursday.

High Surf Advisory for Yap and Koror is expected to expire by
Wednesday. Shortly after on Friday surf heights for the two islands
are expected to increase again to possibly 11 to 12 ft and last
through the weekend.

&&

.GUM WATCHES/WARNINGS/ADVISORIES...
GU...High Rip Current Risk through late Wednesday night for
     GUZ001>004.

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

Marianas: Pavliukoit
Micronesia: Hong
Tropical: Hong