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Area forecast discussion National Weather Service tiyan GU 705 am chst Thursday Jul 2 2015 Synopsis...northeast winds and isolated showers will prevail today. Showers and winds will increase as Chan-Hom approaches the marianas. && Discussion... the main concern is what will Chan-Hom do. The track forecast is still not certain as projections have shifted between a passage to the north of Guam and also to the south of Guam. Despite the early morning prediction of Chan-Hom passing through the Rota channel left the old forecast that shows the storm passing south of Guam. Feel uncomfortable with flip-flopping the track until the models settle down on their predictions. At any rate felt that this did not sacrifice accuracy all that much as the forecast predicts that tropical storm or even typhoon condition are possible for all the islands. Changed the arrival time as the storm has slowed its forward speed. The earlier forecast had Chan- Hom passing Saturday afternoon...now because of the slower speed passage is closer to Saturday night. Winds should start to pick-up Friday becoming breezy Friday night. Tropical storm force winds are possible by noon Saturday with typhoon condition a possibilityby Saturday night. If figuring out what Chan-Hom will do seems complicated then the addition of the circulation south of Guam known as 94w adds more dimensions to that complication. This circulation is still an independent circulation but is expected to be absorbed by Chan- Hom as time GOES on. Mergers are complicated as the interaction of the two may change the track in still unforeseen ways. After chan- homs passage the marianas will be in southwest winds as the storm will drag the monsoon trough north of the local area. && Marine... buoy data showed an east swell over the marianas this morning. There is winds generated along the monsoon trough south of the marianas is pushing waves in this direction generating a southwest swell. Combined seas of 5 to 6 feet today will begin increasing by Friday. Combined seas are projected to reach 15 to 17 feet && Eastern micronesia... a monsoon trough meanders eastward from a circulation...jtwc invest 94w centered west of weno Chuuk near 8n148e through Tropical Storm Chan- Hom centered northwest of Pohnpei near 11n155e and another circulation ..jtwc invest 97w centered east of Majuro near 7n175e to beyond 180 at 7n. Converging fresh to strong southwest winds feeding toward Chan-Hom and the monsoon trough will maintain showery weather near Chuuk and Pohnpei through Friday. Farther east...monsoonal west to southwest winds associated with 97w will also sustain similar conditions near Kosrae and Majuro through Friday. Enhanced by an upper- level trough in the vicinity...deep convection is possible near Majuro tonight and Friday. As Tropical Storm Chan-Hom drifts west-northwestward passing north of Chuuk on Friday...it might merge with 94w which can cause its wind field to expand. If so...wet weather produced by convergent southwest winds will continue over Chuuk through Saturday. 97w and the monsoon trough are also expected to lift slowly west-northwestward over the next couple of days. This should allow weaker monsoonal winds farther south to shift over Pohnpei...Kosrae and Majuro by this weekend. Under this scenario...shower coverage should begin to decrease over these three locations. By early next week...gentle south to southeast trades might return to Kosrae and Majuro with fair weather. However...lingering monsoonal winds can still trigger isolated convection for Pohnpei and Chuuk through Monday. Latest satellite-derived sea heights indicate 9 to 12 feet near Chuuk and Pohnpei states...and 8 to 10 feet across Kosrae and the Marshall Islands. These values are relatively close with ww3 model predictions. Southwest swell and wind waves produced by fresh monsoonal winds will prolong hazardous surf across Chuuk...Pohnpei and Kosrae states through this weekend. These same elements will also cause sea conditions hazardous for small craft across the Marshall Islands...Kosrae until Friday afternoon and Pohnpei...Chuuk through Saturday afternoon. Coincided with a peaking Spring tide cycle... minor coastal inundations are possible along south and west facing shores near Majuro. && Western micronesia... discussion for the Chuuk forecast is included in the eastern micronesia section above due to a similar weather pattern. A strong monsoon trough extends east-southeastward from Luzon passing 13n130e and north of Koror and Yap near 11n to Tropical Storm Chan-Hom centered northeast of Chuuk near 11n155e. Monsoonal winds south of the trough will continue to generate sporadic convection near Koror and Yap through Friday. As Chan-Hom gradually tracks west-northwestward toward the Mariana islands Friday night and Saturday...it will reinforce another monsoonal wind surge across Koror and Yap. Therefore anticipate even wetter weather for both locals through Saturday. Depends on the intensity of Chan-Hom after it has moved over the Philippine Sea north of Palau and Yap early next week...it might still maintain a wet monsoonal regime over the area. Satellite-derived sea heights data trend for the past couple of days reveals rising seas across the Republic of Palau and Yap state. Latest data suggest seas are reaching 10 feet this morning. This is a good indication of rising swell and wind waves caused by persistent monsoonal winds. Expect this trend to continue through this weekend which will prolong hazardous surf and sea conditions hazardous to small craft across the Republic of Palau and Yap state into next week. && Gum watches/warnings/advisories... GU...none. Marianas waters...none. && $$ Ziobro/chan