Thunderstorms!
one crew:
Hold away, if you have the fuel until the weather improves, or off to your alternate.
From long experience with South East Asian Thunderstorms, a rough guide {and it is only rough}is that many storms follow the 30 minute guide, 30 minutes building, 30 minutes at full force and 30 minutes dissipating. The trick is to know which 30 minute cycle it is in when you arrive!.
How many times have we all arrived in less than pleasant circumstances, only to find that a little while later, the sun or moon is out and visible.
Tmb