Tropical storm "Siony" (international name "Atsani") may intensify into a typhoon prior to its close approach or landfall over the extreme part of Northern Luzon this week.
In its 11 a.m. severe weather bulletin on Wednesday, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) said Siony was last observed at 565 kilometers (km) east of Basco, Batanes, packing maximum sustained winds of 85 kilometers per hour (kph) and gustiness of up to 105 kph.
It will likely remain almost stationary in the next 24 hours, then may move generally west towards extreme Northern Luzon.
PAGASA said a landfall scenario over Batanes-Babuyan Island is possible, however "there remains a high degree of uncertainty in the forecast track" due to the quasi-stationary state of Siony.
Siony may further intensify into a severe tropical storm, with maximum wind speed of 89-117 kph, in the next 24 to 36 hours, the State weather bureau said.
A further intensification into a typhoon, with maximum wind speed of 118 to 220 kph, is also likely by Thursday prior to close approach or landfall over extreme Northern Luzon, it added.
As of Tuesday, PAGASA said the combined effects of the northeasterlies, or the cold winds coming from the north, and the trough of Siony will bring light to moderate with at times heavy rains over Batanes, Apayao, Cagayan, and Isabela.
PAGASA reminded the public to remain vigilant against possible flooding, including flash floods, and rain-induced landslides during heavy or prolonged rainfall, especially in areas that are highly susceptible to these hazards.
Meanwhile, tropical storm "Rolly" (Goni) was almost outside the Philippine area of responsibility around noon of Tuesday or 540 km west of Subic, Zambales.
Rolly has no more direct effect over the country's weather.
However, Siony and Rolly may enhance the northeasterlies and bring rough to very rough seas over the seaboards of Northern Luzon.
PAGASA advised that sea travel remains risky over these waters, especially for those using small boats.
Meanwhile, moderate to rough seas will be experienced over the remaining seaboards of Luzon and the eastern seaboards of Visayas and Mindanao.
Mariners of small sea vessels were advised to take precautionary measures when venturing out to sea, while inexperienced mariners were asked to avoid navigating in these conditions.
Metro Manila and the rest of the country will be partly cloudy to cloudy with isolated rain showers due to localized thunderstorms.
Based on the PAGASA's historical data, one to three tropical cyclones may enter or form within the Philippine area of responsibility in November.
Siony is the first cyclone to enter the PAR this month.