Officials issued more mandatory evacuations early Saturday as the forecast for Hurricane Irma turned more bleak for Tampa Bay.

Hillsborough County issued a mandatory evacuation for Zone A, as well as for all residents in mobile homes, starting at 8 a.m.

Pinellas County expanded its mandatory evacuations to Zone B, bringing the total of open shelters to 16. The latest order means all residents in evacuation levels A, B and mobile homes should take shelter by dusk Saturday. The order went into effect immediately.

According to Sheriff Bob Gualtieri, that will affect an additional 260,000 people beyond the people from Zone A who should have already evacuated.

Pasco County issued a mandatory evacuation order for Zone A, which Pinellas County Administrator Mark Woodard said tropical storm force winds will hit Pinellas as of Sunday 2 p.m. and last 24 hours, followed by hurricane force winds at 8 p.m. and lasting nine hours. Add to that rainfall of 6 to 8 inches and a storm surge of 3 to 5 feet, and the reason for the added evacuation is clear.

LIVE BLOG: Latest updates on Hurricane Irma.

Even a slight shift to the west will double that storm surge, Woodard said.

"This is a dangerous, impactful storm," Woodard said during the 11 a.m. news conference at Pinellas County's Emergency Operations Center. He told people in A and B zones and in mobile homes they need to get out right away, adding, "The time for procrastination is over. You must act now."

In response to a question about Zone C, Pinellas officials said they don't foresee any circumstances under which they would order an evacuation of that zone or the ones above it.

"Mandatory means mandatory," said state Sen. Darryl Rouson, whose district includes parts of both counties, at a Hillsborough emergency operations news briefing.

Find your zone

Hillsborough officials said 3,000 residents were in shelters as of Saturday morning, which they expected to sharply increase with the mandatory Zone A evacuation order. Officials said they were trying to protect residents in those areas from storm surge, water driven on shore from a hurricane's winds. Residents who live in flood zones should be prepared to move to higher ground, they said.

"This could be a monster that we didn't expect on the west coast," said U.S. Sen. Bill Nelson, D-Orlando. "And here it comes."

Hernando County officials had ordered mandatory evacuations for residents in zones A and B Friday, including all coastal homes and mobile homes.

Here is the list of Pinellas shelters now open:

• Carwise Middle School, 3301 Bentley Drive, Palm Harbor

• Dunedin Elementary School ,900 Union St., Dunedin

• Clearwater Fundamental Middle School, 1660 Palmetto St., Clearwater

• Ross Norton Recreation Center, 1426 S Martin Luther King Jr., Ave.,

Clearwater

• Sexton Elementary School, 1997 54th Ave. N, St. Petersburg

• Lealman Innovation Academy, 4900 28th St. N, St. Petersburg

• New Heights Elementary School, 3901 37th St. N, St. Petersburg

• St. Petersburg High School, 2501 5th Ave. N, St. Petersburg

• Campbell Park Elementary School, 1051 7th Ave. S, St. Petersburg

• Boca Ciega High School, 924 58th St. S, Gulfport

• Palm Harbor University High School, 1900 Omaha St., Palm Harbor

• Largo High School, 410 Missouri Ave., Largo

• Gibbs High School, 850 34th St. S, St. Petersburg

• Oak Grove Middle School, 1370 S Belcher Road, Clearwater *No longer

accepting pets

Pet friendly general shelters

• Dunedin Highland Middle School (70 Patricia Ave, Dunedin)

• John Hopkins Middle School, (701 16th St. S., St. Petersburg)

Here is the list of general Hillsborough shelters:

• Middleton High School, 4801 N 22nd St., Tampa

• Simmons Career Center, 1202 W Grant Street, Plant City

• Pizzo Elementary School, 11701 Bull Run, Tampa

• Cypress Creek Elementary School, 400 19th Ave NE, Ruskin

• Hammond Elementary School, 8008 N Mobley Road, Odessa

• Sessums Elementary School, 11525 Ramble Creek Drive, Tampa

• Brandon High School, 1101 Victoria Street, Brandon

• Valrico Elementary School, 609 South Miller Road, Valrico

• Summerfield Crossings Elementary School, 11050 Fairway Meadow Road, Valrico

• Greco Middle School, 6925 East Fowler Ave., Temple Terrace

Pet friendly general shelters

• Shields Middle School, 15732 Beth Shields Ways, Ruskin

• Bartels Middle School, 9020 Imperial Oak Blvd., Tampa

• Smith, Sgt. Paul Middle School, 14303 Citrus Pointe Drive, Tampa

• Burnett Middle School, 1010 N Kingsway Road, Seffner

Special needs only

• Strawberry Crest High School, 4691 Gallagher Road, Dover

• SunDome at USF, 4202 E. Fowler Ave., tampa

COMPLETE COVERAGE:Find all our coverage about Hurricane Irma here