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Area forecast discussion National Weather Service tiyan GU 1237 PM chst Wednesday Jul 8 2015 Update... Typhoon Nangka has been tracking more westward over the past few hours. Nangka is located near 15.4n latitude and 150.2e longitude. This has increased to potential for tropical storm conditions to occur at Saipan and Tinian. Therefore as a precaution...have issued a typhoon watch for Tinian and Saipan and their adjacent coastal waters. && Previous discussion... /issued 704 am chst Wednesday Jul 8 2015/ Synopsis... Typhoon Nangka is about 480 miles east-northeast of Guam...while Typhoon Chan-Hom is 835 miles west-northwest of Guam. The marianas are sandwiched between these two systems...in partly cloudy skies...light winds and only isolated showers. Seas are still running 10-11 feet at tanapag buoy at Saipan. Discussion... not much change made to the forecast for now...keeping any tropical storm conditions from Nangka north of Saipan. Models try to bring 30 knots winds down to Saipan as Nangka passes Thursday...but model depictions of this typhoon look too large when compared with what is actually seen on Sat imagery. Will keep a careful watch on the possiblity of heavy showers for Saipan and Tinian on nangka's southern fringe...but again Nangka is larger in the models than in real life. Marine/surf... wave guidance boosts the seas by 2 to 3 feet in northern Saipan waters compared to yesterday...but this appears to be based on a model wind field that is probably too large...and is certainly larger than jtwc credits it with. As a compromise... added a foot to seas Thursday through Friday...which brings seas to 16 feet on the northern fringe of Saipan waters. Otherwise...no major changes to surf or small craft advisories. Surf should diminish on south facing reefs Thursday...but hazardous surf will spread to north facing reefs as swell from Nangka swings around from east to northeast. Tropical systems... on satellite Nangka appears to be headed straight for agrihan on a 300 degree heading at about 15 miles per hour. Jtwc brings it up to super typhoon today...but right now it appears to be going through a glitch in its intensification...eroding on the west side and elongating NNE-SSW. With tropical storm winds only extending out a little over 100 miles and Nangka passing about 180 miles north of Saipan...tropical storm conditions don't seem likely at Saipan unless Nangka veers south or expands...but it is a bit close for Comfort and we will keep a sharp eye on this typhoon. Eastern micronesia... Typhoon Nangka...centered 640 miles north-northwest of Pohnpei... continues to steadily move west-northwestward away from eastern micronesia. Behind Nangka...weak ridging continues to build into the region resulting in fairly dry and stable conditions for all 3 forecast points. Models indicate that the monsoon trough will not begin to reestablish itself over the region until late in the weekend. As a result...fairly dry and pleasant conditions will continue across eastern micronesia through Sunday. Western micronesia... latest infrared satellite data shows all shower activity associated with Typhoon Nangka well to the north of Chuuk this morning. As Nangka continues moving toward the northern cnmi...ridging will build in over Chuuk state. This ridging will maintain a fair weather pattern over Chuuk state through the weekend. Residual cloudiness from Typhoon Chan-Hom will remain over Koror through today and over Yap through Thursday night. As Chan-Hom continues to move off toward the northwest...a broad area of ridging will maintain fair conditions over both Koror and Yap for the next several days. Monsoon generated swell and wind waves will continue to produce hazardous surf on south and west facing shores of Yap and Koror this morning. Seas will continue to subside through the day allowing surf to fall below hazardous levels by this afternoon. && Gum watches/warnings/advisories... GU...high surf advisory until 6 PM chst Friday for guz001>004. Typhoon watch for guz003-004. Marianas waters...typhoon watch for pmz153-154. Small Craft Advisory until 6 PM chst Friday for pmz151>154. && $$ Williams/middlebrooke/kleeschulte