Severe Tropical Storm ''Siony'' slightly intensified as it moved closer towards Luzon Strait placing Batanes and Babuyan Islands under Tropical Cyclone Wind Signal Number 2 , the Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) said on Thursday.

Based on Pagasa's latest bulletin, ''Siony'' was last spotted east of Basco, Batanes with winds of up to 100kph and gusts of 125 kph.

Pagasa said ''Siony'' will continue to move west or west-northwest at 20kph.

Pagasa forecast that the eye of ''Siony'' will likely pass over or near the vicinity of Batanes or Babuyan Islands Friday morning.

“Siony is forecast to reach typhoon category with a peak intensity of 120 km/h by tomorrow morning as it passes near or over the Batanes-Babuyan Islands area,” the weather bureau said.

TCWS Number One is over the northern portion of mainland Cagayan (Santa Ana, Gonzaga, Lal-Lo, Allacapan, Santa Teresita, Buguey, Camalaniugan, Aparri, Ballesteros, Abulug, Pamplona, Sanchez-Mira, Claveria, Santa Praxedes), the northern portion of Apayao (Santa Marcela, Luna, Calanasan), and the northern portion of Ilocos Norte (Adams, Pagudpud, Bangui, Dumalneg, Burgos, Vintar, Pasuquin, Bacarra).

According to Pagasa, after leaving the Philippine Area of Responsibility (PAR) by Friday afternoon or evening, Siony is expected to turn towards the southwest on Saturday morning and accelerate over the West Philippine Sea.

“After exiting the PAR, 'Siony' will gradually weaken due to increasingly unfavorable conditions over the West Philippine Sea associated with a northeasterly surge,” it said. Ella Dionisio/DMS