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.
