I've just added a small new feature in that gives the weather today and the four-day forecast for a bunch of destinations covered on Travelfish. You'll see it in the right column when available. Has a pretty pic, the general conditions and the temperature range in Celsius and Fahrenheit.
You can see some examples here: Ko Samui Chaweng Beach Mukdahan and Hanoi . The info is supplied by Google, who I think in turn grabs it from WeatherUnderground.
Some popular places, notably Ko Tao, doesn't have data, but in those kind of cases, use the "destinations nearby" in the left column to pick a bigger centre nearby (they're ordered by proximity, upto 200km away) to see if you can find the weather.
I wouldn't plan the construction of a house around these snippets, but if you were trying to decide between say Ko Samui and Phuket over the next few days, the weather is looking a bit better on the west coast