862
FXPQ50 PGUM 130756
AFDGUM

Area Forecast Discussion
National Weather Service Tiyan GU
556 PM ChST Thu Jun 13 2024

.Marianas Synopsis...
Partly cloudy skies with isolated showers and gentle to moderate
trade winds prevail across the Marianas this afternoon. Showers are
increasing east of the waters. Ritidian buoy shows seas between 3 and
4 feet, while altimetry shows seas of 4 to 6 feet east of the
islands.

&&

.Discussion...
Some minor changes to the previous forecast. Over the past few days,
partly cloudy skies with isolated showers prevailed during the day,
with mostly cloudy skies and scattered showers at night. This pattern
looks likely to continue tonight through Saturday night. Therefore,
the current forecast now shows scattered showers from around 6 PM
through around 9 AM for the next few days. Meanwhile, a Tropical
Upper-Tropospheric Trough (TUTT) cell is seen to the northeast of the
Marianas. This location puts the Marianas under upper-level
divergence from the TUTT. This divergence will promote the
development of thunderstorms over the region for the next few days as
the TUTT cell continues to move westward. By Sunday morning, the
TUTT looks to be far enough west to bring upper-level convergence
over the Marianas, helping to decrease convection over the region.

&&

.Marine...
No big changes to the marine forecast. Combined seas look to remain
between 4 and 6 feet through the end of the week, building to between
5 and 7 feet for the weekend into next week. This will maintain surf
large enough to produce a moderate risk of rip currents along east
facing reefs. Surf could produce a moderate risk of rip currents
along north facing reefs over the weekend. Gentle to moderate trade
winds will prevail through the beginning of next week. Weak trade-
wind troughs along with a TUTT cell to the northeast of the waters
are expected to bring a few thunderstorms to the waters through
Saturday night. Occasional strong gusts are possible with the
thunderstorms.

&&

.Eastern Micronesia and Chuuk...
A well defined Inter-Tropical Convergence Zone (ITCZ) has developed
across the region extending from the Marshall Islands and all the way
to Chuuk State. Scattered to numerous showers and isolated
thunderstorms extend along the ITCZ and is affecting all the primary
forecast points from Majuro to Chuuk. Added some occasional gusty
winds up to 30 mph over land and 30 knots over the waters to the
forecast at Majuro tonight and then at Kosrae Friday night, based on
the GFS showing locally stronger winds at the locations with the
heavier showers and thunderstorms. The ECMWF did not really show
these locally stronger winds, but past events show the GFS is
typically more aggressive with convective driven winds and usually
picks up this potential sooner than the ECMWF. The GFS then loses
these locally stronger winds after Friday, so did not mention
occasional gusts at Pohnpei or Chuuk at this time. The ITCZ will
shift north and south through the weekend, but not expecting much
change in overall showers and thunderstorm coverage across the region
until early next week, when models start to show signs that the ITCZ
may start to fracture into a series of trough, which will still
support an overall wet pattern across the region.

Altimetry shows combined seas across the region are around 4 to 6
feet, and pushing up to 7 feet east of the Marshall Islands.
Scatterometer data shows winds are gentle to moderate along the ITCZ
with pockets of fresh winds embedded within the heavier convection.
These fresh winds with occasional strong gusts will affect Majuro
tonight and Kosrae Friday night. The previous forecast mentioned seas
decreasing by 1 to 2 ft near Chuuk, Pohnpei, Kosrae and potentially
2 to 3 feet near Majuro by the weekend, but models are not showing as
large of a decrease in the trade swell and wind waves anymore. This
has led to limiting the decrease in seas by about a foot across the
region through the weekend.

&&

.Western Micronesia...
Satellite imagery shows scattered showers and isolated thunderstorms
to the east of Yap Proper and Palau this evening, along a trough in
eastern Yap State, while the main islands of Yap and Palau are
currently partly to mostly cloudy with isolated showers. Winds are
also light and variable at Palau and Yap as a weak trough extends
from the Phillipines towards Palau and then merges with the trough in
eastern Yap State. Previous model runs had showers moving into both
Yap and Palau already, so the current forecast delayed scattered
showers to near midnight for Yap and after midnight for Palau, based
on current satellite imagery and newer model guidance. Also, as the
TUTT cell currently northeast of the Marianas continues to drift
westward and through the Marianas this weekend, the risk for
thunderstorms will increases across Palau and Yap, so made sure
isolated thunderstorms was in the forecast for both locations
starting later tonight and through at least Saturday night. After
Saturday night, models show the TUTT lifting northward which would
help to decrease the potential for thunderstorms on Sunday. As the
ITCZ continues across eastern Micronesia and Chuuk, models depict an
overall wet pattern for Palau and Yap, supported by troughs and trade
convergence that break off from the ITCZ and push westward into
Palau and Yap through at least early next week, along with some
strengthening of the trade winds around both locations.

The buoys near Palau and Yap and altimetry data shows seas around
Palau and Yap are around 2 to 3 feet. Seas are not expected to change
much through the middle of next week, as wind waves and trade swell
are not expected to change much. Winds will remain light around Palau
through at least the weekend, but easterly winds are expected to
become light to gentle at Yap around Saturday.

&&

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

$$

Marianas: Kleeschulte
Micronesia: Schank