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So, what's the difference?


No hurricane is on record as ever hitting the USA's West Coast, and meteorologists know of only one tropical storm that hit California as the 39 mph or faster winds needed to define it as a tropical storm.

Many storms with winds much faster than 39 mph have hit the state, of course, but these have been extratropical storms.

California's one, confirmed tropcial storm came ashore near Long Beach in late September 1939 with 50 mph winds. Since this was before forecasters began naming storms, it has no formal name.

That brings up a question... What's the difference between Tropical and "Extra Tropical"???

The 1:15 p.m. ET, Wednesday, Aug. 22, 1996 GOES weather satellite photo is a water vapor image, which shows the amount of water vapor in the atmosphere using different shades of gray, varying from dry (black) to moist (white).
The blue lines are latitude and longitude lines marked off every 5 degrees.

In the images we see two storms - an extratropical storm east of Florida and Tropical Storm Dolly over Mexico's Yucatan Peninsula at about 20 degrees north latitude and 90 degrees west longitude. Dolly is surrounded by warm, moist air, indicated by the gray shading, in a single air mass. Here, thunderstorms blow up all around the storm's center and latent heat, given off as the water vapor condenses into rain, feeds the tropical system.

The extratropical storm, however, has a narrow black region called a "dry slot" spiraling into the storm's low pressure center from the north. This intrusion of dry air is within a cold air mass astride warm, moist air on the storm's east and south sides. The temperature difference between these two air masses intensifies the storm. A cold front marks the leading edge of advancing cold air on the storm's southern side, while a warm front leads the warm air's move north along and into the storm's eastern side. Where the two meet, thunderstorms can blossom. They are strongest ahead of the cold front and don't surround the system's center as in a tropical cyclone.

From fall through the winter and well into spring, extratropical storms dominate the weather across much of the United States and other parts of the globe outside the tropics. "Extratropical" means the storms originate outside the tropics. These storms move generally west to east across the oceans and continents.

The extratropical storm's center is an area of low atmospheric pressure with winds going counterclockwise in the Northern Hemisphere, clockwise south of the equator. The winds pulls cold air toward the equator from the polar regions and bring warm air toward the poles. The clash of warm and cold air leads to the widespread precipitation the storms bring.

1 - Cold air plunges Southward, forming a cold front along its leading edge.

2 - Warm Air surges northward, forming a warm front along its leading edge

3 - In the Northern Hemisphere winds spin counter clockwise in the "intermix" zone of the two air masses.  This forms a low.  the stronger the low, the stronger the Extra Tropical Storm

Tropical cyclone

  • Forms over a tropical ocean.
  • Center of storm is warmer than the surrounding air.
  • Has no fronts.
  • Strongest winds are near the Earth's surface.

Extratropical cyclone

  • Forms outside the tropics.
  • Center of storm is colder than the surrounding air.
  • Has fronts.
  • Strongest winds in the upper atmosphere.