Tropical Depression Luis maintained its strength Monday morning as it moved slowly over the sea east of Aurora and continued on a track toward Northern Luzon, according to Pagasa.
As of 8 a.m., the center of the tropical depression was located 135 kilometers east of Casiguran, Aurora, with maximum sustained winds of 55 kilometers per hour and gusts of up to 70 kph.
Tropical Cyclone Wind Signal No. 1 remained in effect over parts of Cagayan, Isabela, Quirino, eastern Apayao, eastern Kalinga, eastern Mountain Province, eastern Ifugao and northern Aurora.
Pagasa said Luis was expected to move generally northwestward and could make landfall or pass close to Northern Luzon on Monday evening or early Tuesday.
The weather bureau said the cyclone was forecast to make a sharp turn toward the east northeast after approaching the country and move away from the Philippine landmass.
Forecasters noted that the projected track remained highly uncertain and could still change in succeeding advisories.
Luis was expected to remain a tropical depression before weakening into a remnant low pressure area by Wednesday.
Pagasa said the remnant circulation of Luis could later be absorbed by Typhoon Dolphin, which remained outside the Philippine area of responsibility and had no direct effect on the country.
