Over the past several days, an area of low pressure (Invest 91W) developed within the monsoon trough/ITCZ, generating bands of showers and thunderstorms across the southern South China Sea. As a result, fresh winds extended to the Borneo coast and Malay Peninsula over the weekend. Strong to near-gale force northerly winds also occurred along the northwest side of the low when it intensified this morning. Global models often underdo monsoon winds within these lows and these systems should always be monitored closely for tropical development. The model consensus is that this low will gradually weaken as it drifts west across southern Vietnam and the Gulf of Thailand through Wednesday. The image below is the latest run of the ECMWF, forecasting the westward movement into the Gulf of Thailand, valid Wednesday evening local time in Malaysia. Slightly lower pressure and moderate northerly winds indicate the low.
Cool, dry monsoon winds should inhibit tropical development as the low tracks west across the Bay of Bengal this weekend.
This time of year, a cooler Eurasian continent results in strong high pressure over central Asia and subsequent northeast winds across the East and South China Seas. These winds are referred to simply as the Northeast Monsoon (aka the Winter Monsoon or Boreal Monsoon). When a shortwave trough ejects east across the region, air pressure rises underneath it, leading to cold air surges over the South China Sea. These cold air surges are similar to cold fronts, without the wind shift. The next surge in the northeast monsoon is expected over the northern South China Sea later this week, in response to a 1032mb+ high moving to the east China coast. This will induce gale force winds across the Taiwan Strait.