 The depression strengthened into a tropical storm the next day, and was given the name Fern by the Joint Typhoon Warning Center (JTWC).The storm slowly intensified into a Category 1 typhoon on the Saffir–Simpson hurricane wind scale, according to JTWC.Fern peaked north of Yap on December 26, with JTWC assessing winds of 150 km/h (90 mph), while the Regional Specialized Meteorological Center, Japan Meteorological Agency (JMA) assessed peak winds of 110 km/h (70 mph), just below typhoon strength.