Does the breaker have a little butting on it saying "test"?
If so this is a GFI breaker and it is protecting all the receptacles it feeds. Receptacles in garages and outdoors require this GFCI, or Ground Fault Circuit Interrupter, protection. GFI for short.
I bet one or more of the receptacle on this circuit got wet and are still wet. Check the outside receptacle and if they are wet simply replace them. They cost about a dollar each and if they are more than several years old and get used replacing them will not be a bad idea at all.
IMO it's easier than trying to dry them.
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