Montshire Minute: Hurricanes

Originally aired during the week of September 27, 1999

Monday

Summer is over and fall has arrived - but many people to the south of us are observing another season - hurricane season. Hurricanes usually occur in the North Atlantic from June to November, with most of them in September. While New England tends to avoid direct hits from these tropical storms, our weather is very often affected by them, as we discovered a few weeks ago when Hurricane Floyd dropped in for a visit. On average, between six to eight hurricanes form in the North Atlantic or North Pacific each year. But, as many as 15 have occurred in the Atlantic in a single year. Hurricanes with wind speeds of 74-95 miles per hour are called category one storms - the scale goes up to category five, with wind speeds of over 156 miles per hour. Floyd was right up there in category four.

Tuesday

How do you make a hurricane? Well, assuming you'd want a recipe that unleashes the awesome power of nature at its most violent, you'd start somewhere in the warm tropical waters of the Atlantic Ocean. (Similar storm systems are called cyclones when they occur in the Indian Ocean, and typhoons in the Pacific). Hurricanes need the warm ocean waters, which feed the storms with energy. Then, you'd need a disturbance in the atmosphere which develops into an area of low pressure. The ocean pumps heat and moisture into the storm, causing the warm air in the center of the developing storm to rise faster. The air is pushed out the top like smoke from a chimney - and more air rushes in at the ocean's surface to take its place. This tropical depression can develop into a tropical storm, after which it may graduate into a hurricane.

Wednesday

One of the factors that determines how many hurricanes happen in a given year is a natural force called the conveyor effect, which carries warm Atlantic waters north from near the Caribbean to an area east of Greenland. There, the current sinks deep, moves south, and flows into the southern Atlantic Ocean and beyond. It's the warm, northward-moving surface water - hurricane fuel - that helps produce strong storms. By the time it makes landfall, a hurricane contains lots of moisture, which it unloads in the form of torrential rains lasting for hours. The hurricane weakens as it moves over land because it is cut off from the warm ocean waters that feed it. Friction caused by the rougher land surface also slows the winds down. Hurricanes are usually downgraded to tropical storm status by the time they reach out neck of the woods.

Thursday

When a hurricane bears down on the Atlantic coast, radar systems, satellites, and aircraft give us a steady stream of information about the exact position and severity of the storm. Forecasters have some idea of when and where the storm may make landfall. But it wasn't always that way. Without modern forecasting tools, residents of New England were taken by surprise by the infamous 1938 hurricane which claimed the lives of 60 people. Meteorologists expected the hurricane to hit Miami. When the storm veered away from the southern coast, forecasters assumed it was headed back out to sea. Instead, the storm was moving almost due north, picking up speed and intensity. When it crashed into the New England coast on September 21, it was a category 5 storm with gusts over 200 miles per hour. Montshire's weather exhibit includes some photos of local devastation caused by this storm.

Friday

What's in a name? If you're in the path of a hurricane it can mean a lot. Just mention the name "Floyd" to a Floridian and see what kind of reaction you get. Weather forecasters began giving women's names to hurricanes during World War II. Soon afterwards, The World Meteorological Organization adopted an alphabetical naming system. The first hurricane to get an official name was Able in 1950. In 1979, the WMO included male names on the list, and made up a rotating naming system - it goes girl-boy; girl-boy. Twenty-one names are on the list each year (except names beginning with the letters q, u, x, y and z - sorry Zachary), and the names are recycled every six years. Only the names of really big, impressive hurricanes are retired. When that happens, the WMO chooses a new name to replace it. Some of my favorite names on the 1999 list? How about Wilma, Ophelia, or Vince?