There are three seasons in Thailand:

hot season/summer or “rɯ́-duu rɔ́ɔn (ฤดูร้อน)”,
cold season/winter or “rɯ́-duu nǎaw (
ฤดูหนาว)”
and rainy season or “rɯ́-duu fǒn (
ฤดูฝน)”.

The word “rɯ́-duu (ฤดู)” means season, you also can say “nâa (หน้า)” as a spoken-language such as “rɯ́-duu fǒn (ฤดูฝน)” or “nâa-fǒn (หน้าฝน)” for the rainy season.

To say “Flood” in Thai language is “náam-thûam (น้ำท่วม)”, “náam (น้ำ)” means water, “thûam (ท่วม)” means overflow so flood is “náam-thûam (น้ำท่วม)” and no flood is “náam mâi thûam (น้ำไม่ท่วม)”.

You can’t say “mâi náam-thûam (ไม่น้ำท่วม)” because it is not correct, you can’t put “mâi (ไม่)” before nouns and the word “náam (น้ำ)” is a noun.

Same as “It is raining” or “it rains” is “fǒn-dtòk (ฝนตก)”, “fǒn (ฝน)” means rain, “dtòk (ตก)” means fall so it’s not raining or no rain is “fǒn mâi dtòk (ฝนไม่ตก)” not “mâi fǒn-dtòk (ไม่ฝนตก)”.