MANILA (UPDATE) — Tropical cyclone Ursula (international name: Phanfone) strengthened into a severe tropical storm on Christmas Eve, Tuesday, as it threatened to batter central Philippines, the state weather bureau said.

The country's 21st and potentially last storm this year was 250 kilometers east of Guiuan, Eastern Samar at 4 a.m., packing maximum sustained winds of up to 100 kilometers per hour and 125 kph gusts, said PAGASA.

Ursula could further intensify into a typhoon with 118 to 220 kph maximum sustained winds before it directly hits land in Eastern Visayas on Tuesday afternoon or evening, warned the agency.

Until noon of Christmas Day on Wednesday, the storm will bring occasional to frequent heavy rains over Dinagat, Siargao and Bucas Grande islands, Eastern Visayas, Sorsogon, Masbate, northern and central Cebu, northern Negros Provinces, Aklan, Antique, Capiz, Iloilo, Guimaras and Romblon.

Light to moderate with intermittent heavy rains, meanwhile, will be experienced in the rest of Bicol Region, Quezon, Marinduque, Oriental Mindoro, and the rest of Visayas and Surigao del Norte.

From noon to late evening on Dec. 25, occasional to frequent heavy rains will hit Aklan, Antique, Capiz, Romblon, Marinduque, Oriental Mindoro, Occidental Mindoro, Batangas, and Calamian Islands.

Cuyo islands, Negros provinces, Iloilo, Guimaras, Aurora, and the rest of Calabarzon will experience light to moderate with intermittent heavy rains, added PAGASA.

Residents in all these areas should be on the lookout for potential floods and landslides, said state meteorologists.

PAGASA also raised storm warning signal no. 2 over the following areas, where winds could uproot big trees, peel off roofs and cause "light to moderate damage to exposed communities."

Luzon

• Romblon
• Albay
• Sorsogon
• Masbate including Burias and Ticao islands

Visayas

• Northern Samar
• Eastern Samar
• Samar
• Leyte
• Biliran​
• Extreme northern Cebu (Bantayan and Camotes islands, Madridejos, Santa Fe, Daanbantayan, Medellin, San Remigio, Bogo City, Tabogon, Tabuelan, Borbon, San Francisco, Poro, Tudela, Pilar)
• Northeastern Iloilo (Carles, Balasan, Estancia, Batad, San Dionisio, Sara, Concepcion, Lemery, Ajuy)
• Northern Antique (Libertad, Pandan, Sebaste, Culasi, Tibiao)
• Capiz
• Aklan

Storm signal no. 1 — which means winds could "partially unroof" houses made of light materials and cause "significant damage" to rice crops — was also hoisted over the following areas:

Luzon

• Bulacan
• Bataan
• Metro Manila
• Rizal
• Cavite
• Quezon
• Laguna
• Batangas
• Camarines Sur
• Camarines Norte
• Catanduanes
• Marinduque
• Romblon
• Occidental Mindoro including Lubang Island
• Oriental Mindoro
• Calamian Islands
• Cuyo Islands

Visayas

• Southern Leyte
• Rest of northern Cebu (Carmen, Asturias, Tuburan, Catmon, Sogod)
• Central Cebu (Aloguinsan, Carcar City, Pinamungahan, San Fernando, Naga City, Toledo City, Minglanilla, Balamban, Talisay City, Cebu City, Cordova, Lapu-Lapu City, Mandaue City, Consolacion, Liloan, Compostela, Danao City)
• northeastern Bohol (Inabanga, Danao, Dagohoy, Pilar, Guindulman, Anda, Candijay, Alicia, Buenavista, Jetafe, Talibon, Trinidad, Bien Unido, San Miguel, Ubay, Mabini, Pres. Carlos P. Garcia)
• Rest of Antique
• Rest of Iloilo
• Guimaras
• Northern Negros Occidental (Bacolod City, Bago City, Cadiz City​ Calatrava, Enrique B. Magalona, Escalante City, La Carlota City, La Castellana, Manapla, Moises Padilla, Binalbagan, Hinigaran,​ Isabela, Murcia, Pontevedra, Pulupandan, Sagay City, Salvador Benedicto, San Carlos City, San Enrique, Silay City, Talisay City​ Toboso, Valladolid, Victorias City)
• Northern Negros Oriental (Canlaon City, Guihulngan City, Jimalalud​ La Libertad, Vallehermoso)

Mindanao

• Dinagat Islands
• Surigao del Norte including Siargao and Bucas Grande islands

Some 16,600 passengers were stuck in ports in Metro Manila, Southern Luzon, Bicol Region and Visayas after sea trips were canceled due to the bad weather, said the Philippine Coast Guard.

Ursula is expected to leave the Philippine area of responsibility on Saturday morning, if it continues moving west northwest at 30 kph, said PAGASA.

Christmas storm Usman, one of the deadliest tropical cyclones of 2018, left 156 dead and damaged some 32,000 houses in parts of Luzon and Visayas, the disaster agency reported last year.

Visit the ABS-CBN Weather Center for the latest weather updates.