A rare November tropical storm crawling through the South China Sea has intensified but Hong Kong forecasters said the weather system would not directly affect the city.

Severe tropical storm Tokage was 1,000km south of the city, just west of the Philippine capital Manila, as of midday on Saturday, and moving north with maximum wind speeds of 90km/h.

The storm was expected to continue north before running into the northeast monsoon over Guangdong province, with northerly winds forcing it to turn west around 800km south of Hong Kong, across the middle of the South China Sea towards Vietnam.

Tokage will be only the second storm since 1950 to come near the city in late November. The last time a tropical cyclone affected Hong Kong’s November weather was when Typhoon Krosa hit the city at the start of the month in 2013, prompting a standby signal No 1.

The storm “will gradually dissipate into an area of low pressure in around four days,” Observatory scientific officer Christy Leung Yan-yu said. “It will not directly affect Hong Kong but there could be indirect effects with [the influence of the northeast monsoon over Guangdong].”