The province of Songkhla, with nine deaths, is the most affected.
In total, since November 22, floods have affected more than 660,000 homes in ten regions stretching from Chumphon to the Malaysian border, along the Gulf of Thailand.
This total does not specify the degree of damage suffered, nor the number of people affected.
A previous report, released on Sunday, reported 12 deaths.
In Pattani, Narathiwat, Songkhla and Yala provinces, more than 22,000 people were forced to leave their homes, the government said on Monday.
Thai authorities are forecasting severe weather until Thursday.
Images broadcast by local media showed water entering homes, schoolyards and fields of rubber trees, which are widely grown in the south.
Drainage operations, using large mobile pipes, are underway to lower the water level in certain places.
Suwas Bin-Uma, owner of a chicken farm in Songkhla province, told state TV ThaiPBS that the floods had wiped out his entire flock of more than 10,000 chickens.
“I lost at least three million bahts (83,000 euros),” he assured.
The government is coordinating relief operations on the ground, and has promised to provide 50 million baht (EUR 1.4 million) in aid for each affected province.
Each affected family will also receive 9,000 bahts (250 euros), Bangkok assured.
“There is a team of rescuers who come and distribute a meal once a day,” Abdullah Abu, the head of a village in Yala province, told Channel 7 television.
In his village, the water level reached up to seven meters, he noted.
Floods have also affected neighboring Malaysia, where authorities on Tuesday reported the deaths of a total of five people. More than 94,000 people are waiting to return home, after fleeing from rising waters, according to an official report.
In the Malaysian state of Kelantan, AFP images showed houses surrounded by flooded land, and residents scooping floodwaters from their homes.
Monsoon episodes recur every year in these Southeast Asian countries. However, scientists say global warming is increasing their intensity and may make destructive floods more frequent.
Typhoon Yagi caused widespread flooding in the north of the kingdom in September, as well as in Vietnam, Burma, and Laos, killing hundreds of people.
Thai Prime Minister Paetongtarn Shinawatra recently visited Chiang Rai province (north), particularly affected by flooding, to oversee reconstruction efforts.
In 2011, giant floods affected millions of households in Thailand, causing losses estimated at more than $46 billion, according to the World Bank.
