Following a category two hurricane or a 50-year coastal storm, Beach Road and Eastville avenue would likely be buried under water, and the only remaining access to the Martha's Vineyard Hospital in Oak Bluffs would be Temahigan Road, according to preliminary results of a risk assessment study prepared by an independent consultant.

But even under a worst-case storm scenario, the actual hospital facility would avoid major flooding, the preliminary study suggests.

Woods Hole Group, a coastal science and engineering firm based in East Falmouth, presented the preliminary risk results at a Martha's Vineyard Commission subcommittee meeting this week. The commission is set to review plans for a $42 million new hospital as a development of regional impact (DRI), and has scheduled three public hearing sessions on the project for the first two weeks of November.

The final risk assessment study is due in mid-October, just before the commission begins its formal review. Hospital officials hope to obtain all of the necessary permits by the end of the year, with construction of the 90,000-square-foot, two-story addition to start soon after.

The central issue during the commission hearings is expected to be whether it makes sense to expand and replace the 1972 hospital facility on its existing 13-acre site in the Eastville section of Oak Bluffs, which is located within or near a flood zone and poses concerns about access. The commission in July hired an independent consultant to prepare a report on the risks associated with the location, with the $24,000 price tag to be covered by the hospital.

Leslie Fields, the Woods Hole Group coastal geologist who presented the preliminary results at the subcommittee meeting on Monday, explained that the study will seek to give objective information to the commission about possible risks, and the commission then must decide how it wants to interpret the findings.

"What level of risk is too much?" Ms. Fields asked. "At what point do you say that is not an acceptable risk, and you need to find a better site, or that it is an acceptable risk, and you need to mitigate it?"

The meeting on Monday was marked by visible tension between commission officials and hospital representatives who attended the session, along with about a dozen members of the public. Oak Bluffs emergency management director Peter Martell criticized the scope of the risk assessment study as overly broad.

"How many future unproven problems are we going to crank into this?" Mr. Martell asked. "Look at the last 75 years. The building has been there, and there has not been a problem. But you can create all kinds of scenarios, and the world is going to come to an end."

The meeting also included debate about future rates of sea level rise. Historical data suggests that sea level in the Cape and Islands region is rising by about one foot per century, but some scientific organizations have suggested that global warming will cause an acceleration of the current rates. The independent consultant and commission officials did not agree on Monday which rates to use.

Commission executive director Mark London said that new observations from the National Oceanic and Atmospheric Administration (NOAA) suggest that sea level might rise by as much as three or six feet in the next century, but Ms. Fields remained skeptical.

"It is a subject of a lot of scientific and political debate," she said. "At this point, we at Woods Hole Group are thinking it's too early to tell whether there is going to be an accelerated rate of sea level rise in the future."

Regardless of sea level rise, Ms. Field reported that historical data from the state office of coastal zone management indicates that the eastern shore of Vineyard Haven harbor is eroding at six-tenths of a foot per year. At that rate, in 100 years the Eastville shoreline would be near the edge of Beach Road.

Ms. Fields on Monday said that the group still must identify and profile other possible natural hazards - such as snowstorms or wildfires - and determine their frequency and intensity on the Vineyard. But she acknowledged that the primary concern was flooding caused by hurricanes, northeasters or intense rainstorms.

The study uses two primary sets of flood maps - one that is based on hypothetical events, and is intended to represent maximum flooding in a worst-case scenario, and another that is based on existing tide gauge data, and models the effects of waves and wind to predict inundation during different levels of coastal storms. The commission posted the preliminary presentation, which includes copies of the maps, on its Web site this week.

In addition, Woods Hole Group compiled data from the roughly 100 tropical storms and hurricanes that have passed within 100 miles of the Vineyard in the last 150 years. Ms. Fields calculated the probability of a category one hurricane coming within 100 miles of the Island on any given year to be between 7.5 and 16 per cent, while the annual probability of a category four hurricane is about one per cent.

Ms. Fields also noted that the tracking speed of a passing hurricane often has more of an impact than the actual category or wind speed of the storm, and that storm surge is typically greater on the Cape than on the Vineyard.

"This side of Vineyard Haven Harbor is, relatively speaking, pretty well protected by East Chop," she said of the hospital site.

Some commission members told Ms. Field on Monday that they would like to see flood maps of the entire Island, to put the potential Eastville impacts in a larger perspective. Hospital chief executive officer Timothy Walsh agreed.

"If we could, it would be nice to see the whole Island - which people will be isolated, and can't get out," Mr. Walsh said.