"It's not quite as a significant as predicted at the end of last week but the warning is still valid and relevant".
An ominous forecast graphic by the NHC shows how strong gales from Helene will pound western regions of the United Kingdom on Monday and Tuesday. It will be heavy in many areas with a risk of spot flooding.
The warning says some damage to trees is possible, as are some delays to road, rail, air and ferry transport.
Laura Ellam, deputy meteorologist with the Met Office, said: "Throughout this week, we are expecting to see periods of strong winds across parts of the United Kingdom, as well as some heavy rain".
"Winds are likely to gust to 55-65 miles per hour quite widely in the warning area, with possible gusts of 70-80 miles per hour in exposure".
She is now one of a glut of tropical storms in the Atlantic, with Florence sparking mass evacuations as she heads towards landfall in the USA states of North Carolina, South Carolina and Virginia.
"Winds associated with the storm are now expected to be strongest at sea and along the south and southeast coasts, with winds overland expected to be moderate to fresh, easterly in direction at first, then becoming cyclonic variable as the eye of the storm passes over".
The weather forecast for Wednesday is not part of Storm Helene, which will have moved on, they added.
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The Met Office yellow warning asks people living in affected areas to be aware of the dangers the weather could bring.
The warning to motorists came after Met Eireann extended a Status Yellow - Rainfall warning to five counties, Galway, Mayo, Sligo, Leitrim and Donegal, which will remain in place from 13:00 on Monday, 17 September until 05:00 on Tuesday, 18 September.
"The colour might change as we get closer to the time".
Tonight, a band of showery rain will clear east across the region this evening, then dry by midnight with some clear spells, and with winds easing.
A smaller hurricane dubbed Isaac is reportedly heading for the Caribbean, while Hurricane Helene - now also in the Atlantic - is forecast to track towards the UK.
Winds have reached around 60mph along exposed coasts of the South West and Wales this morning and it has been a noticeably warm start to Tuesday, with temperatures around 19 or 20C.
"Helene is still over the Atlantic but it's weakening and we're a lot more confident of what's going to happen", the spokesman said.