What Is An Extra-tropical Cyclone?

[Harbor_Pilot]

WHAT IS AN EXTRA-TROPICAL CYCLONE?

In the Storm Warnings Forum, in the post, “Typhoon 04w - Man-yi - Northwest Pacific Ocean”, started on 7 July 2007 Here

In post # 20, I posted Warning NR 021. (**) In that warning, near the end, in the remarks block is a comment:

TY 04W WILL COMPLETE EXTRATROPICAL TRANSITION BETWEEN TAU 48 AND TAU 72.

Perhaps the best short answer I found is from USA Today:

Extratropical storms are major weather makers

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. A 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.

How tropical and extratropical cyclones differ

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.

SOURCE {full article with links}: Here

Harbor_Pilot: Typhoon 04W - Man-Yi started as a Tropical Depression, formed as a Tropical Cyclone (over a tropical ocean) and is predicted to transition to an Extratropical Cyclone within 48 - 72 hours of the most recent report; or meeting the last 3 bullet criteria of an Extratropical Cyclone.

A more technical explanation of Extratropical is provided by NOAA:

An extra-tropical cyclone is a storm system that primarily gets its energy from the horizontal temperature contrasts that exist in the atmosphere. Extra-tropical cyclones (also known as mid-latitude or baroclinic storms) are low pressure systems with associated cold fronts, warm fronts, and occluded fronts.

Tropical cyclones, in contrast, typically have little to no temperature differences across the storm at the surface and their winds are derived from the release of energy due to cloud/rain formation from the warm moist air of the tropics.

Structurally, tropical cyclones have their strongest winds near the earth's surface , while extra-tropical cyclones have their strongest winds near the tropopause - about 8 miles (12 km) up. These differences are due to the tropical cyclone being "warm-core" in the troposphere (below the tropopause) and the extra-tropical cyclone being "warm-core" in the stratosphere (above the tropopause) and "cold-core" in the troposphere. "Warm-core" refers to being relatively warmer than the environment at the same pressure surface ("pressure surfaces" are simply another way to measure height or altitude).

Often, a tropical cyclone will transform into an extra-tropical cyclone as it recurves poleward and to the east. Occassionally, an extra-tropical cyclone will lose its frontal features, develop convection near the center of the storm and transform into a full-fledged tropical cyclone. Such a process is most common in the North Atlantic and Northwest Pacific basins. The transformation of tropical cyclone into an extra-tropical cyclone (and vice versa) is currently one of the most challenging forecast problems. {***}

Source Article with graphical depictions and references: Here

Wikipedia, the free encyclopedia, has a rather extensive entry on this topic: Here

*** Typhoon 04W - Man-Yi's evolution, and forecast is an example of this paragraph.

Jeff

** EDITED

In reference to the 4th line from top: This continues in the next post, and likely will for the next several weather updates. Standby and watch how it evolves.