Came to a stop today and noticed my radiator blowing steam, my coolant level hasnt budged from the 'max' so the coolant is fine, its lashing down with rain today so wondering if it could just be that, any ideas?? (fiesta 53 reg)

Obviously overheating, First job is to check the thermostat.

Is it though? My thermostat has gone bad before and the coolant tank lost the majority of its coolant directly from the pressure cap at the offside part of the bonnet, which left me with close to no coolant at all, in this case though, there was steam coming from my radiator but my coolant tank was full, i had steam coming from under the bonnet a few months ago under heavy rain, this time from the manifold, upon inspecting it closer it was a rubber seal that had gone bad which was allowing the water to drip, if a car is overheating and steaming it doesnt keep its coolant?

If its only happening when it rains is it because somehow the rain is getting through via the radiator grill or in under the bonnet and hitting the hot radiator or a top hose, or the exhaust manifold plus any thing else that may be hot.

Had it out today in the dry and it was fine, no loss of coolant, no puddles under car or leak stains on the radiator, no steam after fully heated engine, it seems that rain has got in somewhere, no idea where though, it was pretty bad weather up here yesterday so maybe heavy rain getting blown in by the wind, who knows