A yellow warning for rain is in place in both counties until 06:00 on Monday
Waves whipped up by strong winds lash a sea wall in Penzance
More than 3,000 properties are without power in Devon and Cornwall amid strong winds.
More than 2,000 properties are without power in Devon and Cornwall amid strong winds.
A Met Office, external yellow warning for wind was in force in Cornwall until 11:00 GMT, while a separate yellow warning for rain is in place in both counties until 06:00 on Monday.
Cornwall has had 883 properties affected, along with 1,195 in Devon.
National Grid said more than 2,000 properties in Cornwall and more than 1,000 in Devon were without power.
Drivers have been warned against all but essential travel in Cornwall, with yellow wind warnings in place until 17:00 GMT and a yellow warning for rain for some parts of east Devon until 06:00 on Monday.
A gust of 79mph (127km/h) was recorded in St Mary's in the Isles of Scilly.
There are reports of roads blocked by landslides and fallen trees and some train services have been cancelled.
A landslide blocks the road between Tavistock and Lamerton
An 82mph (131 km/h) gust was recorded in Predannack, south Cornwall, on Sunday morning.
National Grid said thousands of customers had been reconnected to their electricity supplies after more than 8,000 were affected at one point.
Train services running to and from Crediton and Barnstaple in Devon were cancelled due to flooding, said Great Western Railway (GWR), with disruption expected to last until the end of the day.
Trains were also cancelled between Par and Newquay in Cornwall with replacement bus services.
A Ryanair flight from Malaga to Newquay had to divert to Gatwick.
A landslide blocked the road between Tavstock and Lamerton in Devon, while fallen trees blocked a number of other roads around Devon and Cornwall.
As it happened: Storm Herminia hits the South West
Trees have fallen and are blocking roads like this one on the A381 in Thurlestone
Trees have fallen and are blocking roads like this one on the A381 in Thurlestone
A Ryanair flight that was expected to land at Cornwall Airport Newquay at 07:35 was diverted to London Gatwick, with other flights delayed, said the airport, external.
Met Office meteorologist Tom Morgan said it was going to be "wet and windy over the next few days, in southern parts of the UK in particular".
At Exeter Airport flights to and from Belfast and Jersey have been cancelled.
He said: "In most parts of the UK, we're going to have some very wet and at times also very windy weather over today and Monday.
On the roads a fallen tree has blocked the A39 at Falmouth Melvill Road, between Holywell Road and Mill Lane and westbound at Camelford.
"But, from Tuesday onwards, I'm expecting it generally to stay fairly changeable... some showers at times and quite windy, but not as disruptive as it has been – I think, overall, probably warnings are less likely from Tuesday onwards.
A tree has also fallen in the north-bound carriageway of the A380 Telegraph Hill, said Devon Highways, external.
"Certainly tonight in the south east of the UK, we could see some briefly very strong winds, and we could also see some very strong winds across Cornwall and Devon tomorrow in particular."
National Rail said there would be no trains to and from Newquay until about 13:00 GMT.
As,mit happned
Strong waves were seen along the coastline in Cornwall
The strongest gusts so far have been recorded in St Mary's in the Isles of Scilly 79mph (127km/h) and at Berry Head in Devon 68mph (109km/h).
Much of Cornwall is gusting over 60 mph (96km/h).
It is expected the strongest winds will transfer eastwards in the next few hours.
While the peak gusts are expected earlier in the day, it is still expected to remain windy.
Tamar Bridge was closed to high-sided vehicles but it has since reopened, Tamar Crossings said on X, external.
Maggie Howell from Falmouth Coastguard said people should stay away from coastal areas.
"Further out at sea it might have had worse conditions, but it's looking really, really bad out here this morning," she said.
"Don't go trying to go wave watching or anything like that because not only are you risking yourself, you're also risking the people that will come out and try to help if you get into trouble."
Great Western Railway is advising passengers to check before they travel and take extra care while travelling to and from stations.
Cobble Corner in Cornwall has been closed due to roof slates falling off buildings
Devon Highways advised drivers to be alert for any fallen trees and potential flooding.
Andy Cole, from Devon Highways, said: "On our minor network there's a bit of risk on those corners, those blind bends where you come across some debris, a tree branch or even a tree or flood water.
"We just ask the drivers to take extra time, to take extra care and just be aware of what could be around the corner."
Paddy Cochran, also from the coastguard, added: "We've seen the destructive force over the last couple of days, with a number of caravan parks getting properly smashed and all these kind of mini tornadoes running through villages and stuff like that, so just exercise caution and no unnecessary risk please."
On Monday, it is expected the winds will once again pick up, potentially gusting 60-70mph (96-112 km/h) for the duration of the day.
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