Slight change in strength today as Tropical Storm Nepartak churns southwest of the Mariana Islands. The Tropical Storm Warnings and Watches that were posted for portions of Micronesia, along with a Small Craft Advisory for the Marianas, have been cancelled.
Where is it Now?
Tropical Storm Nepartak remains southwest of the Mariana Islands with convection extending through Yap State of Micronesia. The center of circulation is located 385 km west-southwest of Hagatna, Guam or about 490 km northeast of Colonia, Yap. The storm has increased in forward motion–now moving toward the northwest at 30 km/h–as the steering currents have intensified. As of 0600 UTC, Japan Meteorological Agency has noted that the winds have further intensified to 85 km/h with higher gusts near typhoon force at 120 km/h. Central pressure is decreased to 994 hPa. Current Nepartak is outside of the Philippine Area of Responsibility (PAR), but is forecast to do so on Tuesday. At that time, PAGASA will christen it with the name “Butchoy.”
Nepartak is taking advantage of warm ocean waters and ample outflow aloft. Both the Japan Meteorological Agency and the Joint Typhoon Warning Center intensify the storm steadily over the course of the weak, with JTWC presenting a slightly stronger forecast when taking 1-minute vs 10-minute winds into consideration. JMA forecasts Nepartak to become a severe tropical storm later tonight or early Tuesday morning before entering the PAR. While JTWC forecasts typhoon status on Tuesday, JMA holds out until early Wednesday morning. At this time, gales are forecast for the Batanes Group of the Philippines on Thursday, while strong typhoon force winds are forecast to affect Taiwan and the far southern Ryukyu Islands late Thursday into Friday.
The Forecast Track
Nepartak will continue to track northwest along the southwest periphery of the subtropical ridge. The challenge in the forecast will be how a mid-latitude trough affects this subtropical ridge. As a result, the placement of this ridge will govern if Nepartak heads closer to the Ryukyus versus a more westerly track toward Taiwan. The extended forecast (outside of the official 5-day track) presents a few different scenarios, again based on the placement of the subtropical ridge. Western Japan, the Korean Peninsula, and eastern China will need to monitor this cyclone as well.