Fueling wanderlust hurricanes

Q: Do hurricanes stay near where they form?   William, Albuquerque, New Mexico

This weather satellite image of Hurricane Floyd, from September 15, 1999, shows the immense size of the storm, stretching from Florida to Canada. [NASA]

A: No. Hurricanes don’t stay local. Many form off the west coast of Africa. Some start off the northeast coast of South America and a few in between the two continents. A hurricane that stays over the ocean (not making landfall) can travel thousands of miles — from West Africa to north of New York State and beyond. They travel slowly, relative to land travel — about as fast as you ride a bike — east to west and a little north. Air currents propel them like flotsam in a raging river. Most die in 10 days.

Q: When is the hurricane season? William, Albuquerque, New Mexico

A: The main season for hurricanes is late summer to fall. Most hurricanes happen in September, when ocean waters are warmest. On the average, August, September, and October get about 26%, 48%, and 17% of the hurricanes. These months have 91% of the total.

When hurricanes occur, on the average. [April Holladay]

Further Reading:

NOAA: Hurricane research division’s frequently asked questions

Q: How does the energy associated with hydrogen bonds fuel hurricanes? Kristie, Plano, Texas

A: Hydrogen bonds fuel hurricanes by releasing latent heat.

Water is a strange substance with unusual properties due solely to tiny charges surrounding each water molecule. These charges produce hydrogen bonds.

A water molecule (H2O) is made of two hydrogen atoms and one oxygen atom. It has no net charge — positively- charged protons balance negatively-charged electrons.

The "balance", however, is imperfect. The molecular charge does not neatly cancel everywhere in space. Instead, out on the fringes, the oxygen electron cloud somewhat overpowers the electron cloud of the hydrogen. So the molecule ends up with a slight positive charge about the hydrogen atoms and a slight negative one about the oxygen atom.

The tiny charges of one water molecule attract those of another. One slightly positively-charged hydrogen atom of a molecule (red molecule in the figure) bonds with the slightly negatively-charged oxygen of another (black molecule). The other "red" hydrogen atom bonds with the oxygen of still another molecule (blue). In this way, water molecules cling to each other throughout the liquid.

Three water molecules clinging together with hydrogen bonds (shown by gold lines). [April Holladay]

That’s hydrogen bonding — a subtle attraction based on partial charges. Subtle but powerful. It helps fuel hurricanes.

How? Imagine September’s warm Atlantic Ocean, off the northwestern coast of Africa, near the windy dry Cape Verde Islands. The sun beats down heating the surface water. Consequently, water molecules move faster and thereby break hydrogen bonds. The sun provides the large energy needed to bust a molecule free of its bonds with surrounding molecules and to vaporize it.

It escapes the clinging water surface and enters the air above as a gas. In other words, the molecule evaporates. Evaporated molecules carry the bond-breaking energy with them as potential energy (called latent heat).

Denser heavier air collapses into the space occupied by the water vapor, pushing the water vapor up. As the vapor rises, it cools because, it expands into the thinner air. The molecules slow. Eventually, they slow enough to re-associate and form a liquid — clouds or rain.

The molecules then release latent heat energy. This released energy drives hurricanes. The latent heat warms the surrounding air, which causes it to expand. The thinner air causes a low-pressure area. Denser air rushes into the low-pressure area, creating winds. The winds spiral inward (due to the motion of Earth rotating on its axis) and evaporate even more water. The process feeds on itself, escalating into a horrific storm — a hurricane.

Further Reading:

National Oceanic and Atmospheric Administration (NOAA): Active tropical cyclones

Northland Community and Technical College: Hydrogen bonding in water — animation

Fox6.com: Hurricane Center

NOAA: Hurricane basics

WeatherQuestions.com: What causes hurricanes

(Answered Sep. 10, 2004)

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