Krabi Province

Krabi Province covers a section of Thailand's Andaman Sea coast where the geological drama is immediate and hard to ignore. The limestone karst towers that rise from the sea around Railay and Koh Poda are the same formation that continues north into Phang Nga Bay and south into the Koh Lanta archipelago — a drowned karst landscape built over tens of millions of years and now partly submerged by the Andaman Sea. The tidal regime here is semidiurnal, with two highs and two lows per day and a spring range of 2.5 to 3.0 m. This is a meaningfully larger range than the Gulf of Thailand experiences across the Malay Peninsula — the Andaman Sea has better exposure to the Indian Ocean tidal wave. The practical consequences are visible at every beach in the province. At spring low water, wide tidal flats expose. Rock platforms around headlands become walkable. Long-tail boats struggle to land at certain beaches and must anchor offshore with passengers wading. Mangrove channels that are navigable on a mid-flood become impassable mud at low spring. The narrow passages between karst towers concentrate tidal currents; in the Railay channels and the approaches to Ao Nang, flow can reach 1 to 2 knots at spring ebb and flood. Those currents matter to kayakers and snorkellers more than to long-tail boat passengers, but everyone benefits from knowing the tidal window. The monsoon seasons divide the Andaman coast: the NE monsoon (November through April) brings dry weather and light northeasterlies that make the Andaman's west-facing beaches calm and blue; the SW monsoon (May through October) reverses the pattern with heavy rain and persistent westerly wind that raises significant swell. Many tourist businesses on the islands close or scale back from June through September. The Thai Meteorological Department (TMD) is the authoritative forecast source for tides and weather on the Thai Andaman coast.