Updated: 1:00 AM ChST on October 21, 2014
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Area forecast discussion National Weather Service tiyan GU 646 PM chst Sat Nov 1 2014 Marianas synopsis... tropical storm nuri at 13n133e is moving very slowly farther away from the marianas. Ascat analysis indicates a monsoon trough runs eastward from nuri across our forecast zones...then southeastward through a weak circulation at 14n148e to end north of Pohnpei at about 9n155e. Radar shows only isolated showers across the radar coverage area. Satellite shows convective clouds in a band from across Saipan and Tinian southeastward to north of Pohnpei. VAD gradient winds are from northwest at 5 knots. && Discussion... unsettled weather will continue across the local area. Most models indicate as tropical storm nuri eventually moves toward northwest the monsoon trough will gradually drag across the Mariana forecast zones. GFS indicates the weak circulation near 14n148e will also move toward northwest across the Tinian/Saipan area...and could produce periods of heavy rain. This will all need to be monitored carefully. Longer range model solutions indicate a drier easterly flow will arrive later next week perhaps by Wednesday or Thursday. && Marine... slow-moving tropical storm nuri will likely intensify and generate large swell that will affect Western Shores of the marianas in the coming days. A high surf advisory might be needed by Wednesday and combined sea conditions could also approach Small Craft Advisory criteria by Thursday. && Eastern micronesia... light to gentle trade winds along with middle-level dryness are going to maintain fair weather for Chuuk...Pohnpei until Monday...and Kosrae through Sunday morning. Farther east...two trade disturbances can be seen near the western Marshall Islands at 167e and east of Majuro at 175e. The remnants of the first disturbance could bring a few showers to Kosrae Sunday evening...and to Pohnpei and Chuuk Monday and Tuesday. The second disturbance is approaching the Marshall Islands and will increase shower coverage there later tonight. This same disturbance will progress westward and affect Kosrae...Pohnpei and Chuuk near midweek. Latest ascat satellite imagery reveals a near-equatorial trough between 5n and 10n stretching eastward from near the date line to beyond 160w. This feature is expected to migrate westward and prolong showery weather for the entire region through midweek next week. Long-period but small south swells generated by a storm system near New Zealand will arrive at the Marshall Islands by Sunday morning. Since the tide cycle will be at the minimum levels for the next couple of days...no hazardous surf or coastal inundations are anticipated. && Western micronesia... being under a similar trade-wind regime...reasoning for the Chuuk forecast is included in the eastern micronesia section above. Converging southwest to south winds feeding into tropical storm nuri will keep sporadic convection near Koror and Yap this evening. As nuri tracks northwestward farther away tonight...this convection will also shift north of both locations by late tonight. By Sunday...a ridge of high pressure just west of Chuuk near 6n148e will build westward and promote partly cloudy skies for the area. However both the GFS and European model (ecmwf) are hinting the monsoon trough might reform just north of Koror and Yap around midweek. If so...things could become unstable again...therefore have added mostly cloudy skies to the long-term forecast. && Gum watches/warnings/advisories... GU...none. Marianas waters...none. && $$ Ziobro/Simpson/chan