Area Forecast Discussion
Issued by NWS
FXPQ60 PGUM 250640
Area Forecast Discussion
National Weather Service Tiyan GU
445 PM ChST Mon Jul 25 2016
An upper-level low can be seen east of Saipan near 16N149E. A
surface trough is also visible near 152E. Isolated thunderstorms
have been flaring up near these two systems since early this
afternoon. A tropical disturbance located farther southwest near
6N142E has been generating convection south of 10N.
Based on the motion of the upper low and surface trough, wet
weather associated with them should enter the Marianas coastal
waters near midnight. As observed from late last night to early
this morning, diurnal cycle had enhanced scattered showers near
these systems. Expect this process to repeat late tonight and
bring scattered showers to the Marianas thru noon Tuesday. An
upper-level ridge near the Northern CNMI is going to keep the
upper low just northwest of Saipan after Tuesday. This will
maintain the chance of thunderstorms across the area thru midweek.
Models are developing the tropical disturbance currently near
6N142E over the next few days as it tracks west-northwestward into
the Philippine Sea. If so, converging southeast winds feeding
toward the disturbance might form over the Marianas this weekend
which can create more instability.
A light trade-wind swell will sustain combined seas of 2 to 4
feet thru this weekend.
Showers and thunderstorms have reached Chuuk this evening and
models suggest showers will persist through tonight before
tapering off Tuesday morning. Majuro and Kosrae have seen fair
weather today and clouds are now beginning to clear out at
Pohnpei. Satellite imagery shows a trade-wind trough crossing the
Date Line with showers nearing Majuro. Wet weather will affect the
southern Marshalls tonight and gradually spread west bringing
periods of cloudiness, isolated showers and thunderstorms to the
region through the latter week.
Reasoning for the Chuuk forecast can be found in the Eastern
Micronesia discussion above.
A disturbance southeast of Yap near 5N141E continues to drift
westward. Have increased shower coverage at Yap beginning Tuesday
night as this system approaches. Models keep most showers just
north of Koror initially, but models, particularly the ECMWF, show
some development of monsoonal southwesterlies near or just west of
Koror, which will increase the showers and thunderstorms in the
area. Both GFS and ECMWF hint at slow development of the
disturbance after it moves west of Yap and Koror. Slightly quieter
weather is expected over the weekend, but weak low-level
convergence will keep isolated thunderstorms in the area.