Track rain across Surat Thani in real time with Rain Viewer, a hyperlocal rain radar app, updated every 5 minutes, street by street.
Rain in Surat Thani arrives from two directions depending on the time of year. From May to October, the southwest monsoon pushes weather in off the Gulf. From October to January, the northeast monsoon turns the province wet again — making Surat Thani one of the few places in Thailand with no reliable dry escape. A heavy cell stalling over the mainland can cancel Koh Samui ferry services for an entire day, leaving passengers stranded at Donsak pier with no warning.
The Tapee River, which runs through the centre of Surat Thani town, floods repeatedly during peak northeast monsoon events. The town centre, the night market strip, and the bus terminal area have all been inundated in documented events. The flooding arrives from upstream when heavy rain falls in the hills to the north, not always when it's raining at the pier.
Rain Viewer shows you cells forming over the gulf hours before they reach the coast, with street-level precision across the pier, the town, and the roads in between.
The first wet season brings daily rain from the Gulf, with peak intensity in September and October. Storms are often afternoon-weighted and can be intense, though the northeast season is typically heavier.
Surat Thani's heaviest and most sustained rainfall. Multi-day events with 200–300mm in a few days are documented. Generic forecasts consistently underestimate the intensity of these events.
The calmest window, though even in March isolated showers can develop.

One tap, and the rain at that precise spot tells its own story—showing intensity, precipitation type, cloud and air temperatures, and live national alerts, while making even the smallest rain pockets easy to identify and compare.
The ferry to Koh Samui takes 1.5 hours across open water. A squall that forms over the Gulf can close this route for hours. Seeing the storm track before driving 30km to Donsak saves a wasted journey.
The Tapee River flood zone covers the night market area during serious events. Seeing a heavy upstream cell on the radar before the water rises lets drivers reroute before the low roads are impassable.
Surat Thani is Thailand's largest rubber-producing province. Latex tapping is suspended when it rains — workers monitor the radar to time tapping windows.
The Koh Phangan pier approach is exposed to northeast swell. During November–January, departure windows matter. Real-time radar tells operators and attendees whether the crossing is workable.
Rain Viewer combines signals from radar stations across southern Thailand for Surat Thani. From here, you can also track rain developing in Nakhon Si Thammarat, Chumphon, and Krabi — useful if you're driving the route to Donsak or planning a crossing to Koh Samui.
“A little overenthusiastic at times with rain predictions, but it's accurate and spot on for radar images, and it's the one radar app I've kept and not uninstalled”
Duncan Stewart
I must update my feedback once again – this is still the best brain app in the app store. The issue I was experiencing was with my phone, not this top-tier app. One feature I particularly like is the widgets.
Jim Tigs
Every 5 minutes. During the northeast monsoon — when conditions can deteriorate rapidly — this near-real-time update is the most useful tool available.
Briefly — February through April is the quietest window. Surat Thani sits in a transition zone where both monsoons reach it, making it one of Thailand's wettest provinces on an annual basis.
Bangkok is sheltered from northeast monsoon rain by the Gulf's western orientation. Surat Thani's coast faces northeast — directly into the incoming monsoon flow — which funnels moisture onto the eastern Gulf coast between October and January.
Rain Viewer shows storm cells crossing the Gulf and approaching the Donsak–Koh Samui route in real time, with direction arrows showing movement.
Surat Thani's rain arrives from two directions and doesn't follow Bangkok's forecast. The map updates every 5 minutes — often 2–5 minutes faster than other apps — so by the time a northeast monsoon cell is crossing the Gulf toward Donsak, you've already seen it coming.
Rain Viewer Essential gives you:
A 7-day forecast tells you November will be wet. Rain Viewer tells you whether the Gulf is clear enough to drive to Donsak now or wait three hours.
Track rain in Surat Thani — free
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