Map from Google - Songkhla

In Songkhla (or Singgora), a city in southern Thailand, the climate is tropical, hot and humid all year round, with a rainy season, due to the monsoon, which lasts from May to January, but has a pronounced peak between October and December, ie in the period of the "retreating monsoon", while from June to September, and usually also in January, the rains are not too abundant. In the short dry season, from the middle or the end of January to April, some showers are still possible.
Precipitation amounts to about 2,200 millimetres (87 inches) per year. The rains are particularly abundant in the last months of the year, because at that time the monsoon comes from the northeast (retreating monsoon), directly affecting the coasts exposed to the northeast, therefore the eastern part of peninsular Thailand. Typically, the worst month, with real torrential rains, is November, but sometimes they can occur also in October, December and the first part of January.
Here is the average precipitation.
Average precipitation - Songkhla
SongkhlaJanFebMarAprMayJunJulAugSepOctNovDecYear
SongkhlaJFMAMJJASONDY
Prec. (mm)15560609012010095951053155754402210
Prec. (in)6.12.42.43.54.73.93.73.74.112.422.617.387
Days1477101412121314222320168

The temperature is high throughout the year, however, it's slightly lower from November to January, when highs hover around 29/30 °C (84/86 °F); the heat is annoying due to humidity, also because behind the town there is a plain with some lakes (which are actually lagoons), which provide additional heat and moisture. From March to October, there can be hotter days, with peaks of 35/37 °C (95/99 °F). Luckily, sea breezes blow.
Here are the average temperatures.
Average temperatures - Songkhla
SongkhlaJanFebMarAprMayJunJulAugSepOctNovDec
SongkhlaJFMAMJJASOND
Min (°C)232424242424242423232424
Max (°C)303132333333333332313029
Min (°F)737575757575757573737575
Max (°F)868890919191919190888684

The amount of sunshine in Songkhla is good from February to April, that is, in the driest period, but it's not scarce even in the other months, because the rains occur in the form of showers and downpours, which usually do not last long; only from October to early January, that is, in the wettest months, there can be more prolonged cloudy periods.

Songkhla, like other areas of Thailand, can be affected by tropical cyclones, from May to November, although the Gulf of Thailand is a relatively sheltered area, in which cyclones are quite rare and besides they are rarely intense.

Songkhla

For swimming, the sea is warm all year round, as you can see in the following table.
Sea temperature - Songkhla
SongkhlaJanFebMarAprMayJunJulAugSepOctNovDec
SongkhlaJFMAMJJASOND
Sea (°C)282829303030292929292928
Sea (°F)828284868686848484848482

When to go

The best time to visit Songkhla goes from late January to April, being normally the least rainy, with a preference for February, because it is, albeit slightly, the least hot. In January, depending on the year the rains may be more or less abundant, in particular in the first half, when at times they can still be torrential. In summer, in June, July and August, there can be long periods without rain and with an intense heat, with highs around 35 °C (95 °F), while at other times there can be showers, more or less intense, almost every day; furthermore, as mentioned there is a risk, albeit not high, of the passage of tropical cyclones.