The fire to Fingal's south-east was caused by spotting embers from the deliberately-lit Mangana Road fire and has spread "quickly" in the past 48 hours.

The area has experienced below average rainfall for the past 12 months, and "very much below average" rainfall for 36 months.

BOM meteorologist Alex Melitsis said light sea breezes on Friday are offering some reprieve for fire conditions, but that will change on Saturday.

MORE ON THE FINGAL FIRES:

"Tomorrow, what we see is a hot, north-westerly air stream develop that will bring high temperatures and strong winds to much of the eastern parts of Tasmania," he said.

"We're expecting to see wind strengths of around 30 to 40 kilometres per hour across that area, and temperatures into the mid-30s around parts of the Fingal Valley and East Coast.

"A cooler westerly change is expected to cross in the afternoon. At this stage, the winds will shift westerly through the early part of the afternoon, about 2 to 3pm."

Mr Melitisis said the fire danger is expected to be very high from late Saturday morning and for most of the afternoon, but conditions are likely to be much different on the floor of the Fingal Valley.

He said cooler afternoon winds will retain relative humidity.

Despite hot and windy conditions, fire danger is not expected to reach extreme levels experienced last Monday and in other parts of Australia.

Beyond that, the East Coast can expect moderate conditions once the risks of Saturday have passed. Temperatures will drop, before warming up again later next week.

Last month, Fingal Valley residents voiced their concern at the drying up of the St Paul's River, which was experiencing the lowest water discharge on record.

Mr Melitsis said satellite images showed the extent of dryness throughout the East Coast region, including the bush areas that could be impacted by the Fingal fire on Saturday.

"It's just bone dry out there," he said.

The TFS says it has a strategy if the fire reaches Douglas-Apsley National Park. The park will be closed on Saturday and residents in the Bicheno region are advised to read the community bushfire protection plan here.