Why hurricanes weaken over land

Investigate TV. Gray DC Bureau. Breakdown: Why hurricanes weaken when moving across land. By Ron Childers. Updated: Oct. Share on Facebook. Email This Link. Share on Twitter. Share on Pinterest. Share on LinkedIn. Most Read. Shooting at Margaritas restaurant leaves one dead. Why does the appearance of the clear area called an "eye" form when wind speeds around the eyewall at the surface exceed hurricane strength? The centrifugal effects on air "attempting" to circulate cyclonically into the small diameter say, 50 miles or so cyclone center will not be able to move across the isobars when wind speeds approach 70 mph or so.

As a result, divergence aloft will be uncompensated for by air moving laterally into the low at the base of the storm. If this went on indefinitely, a vacuum would form at the surface. The atmosphere compensates for this by sinking from high levels to low levels, resulting in a cloudless, warm, calm storm center known as the "eye". What is the storm surge and why is it associated with great loss of life and great damage in coastal sections? The storm surge is an abnormal rise in sealevel due to two effects.

First, a minor effect is the fact that the very low pressure at the center of hurricanes causes an upward bulge in the ocean at the center of the storm.

Thus, the ocean levels are higher there than in the surrounding areas, often by a matter of 5 feet or so. In addition, the major effect has to do with the augmented winds on the right forward margin of the storm physically pushing the ocean against the coastline for a storm moving from southeast to northwest. The combination of these two effects makes, in particular, the forward right quadrant of a hurricane very prone to significant storm surges, sometimes of nearly 25 feet or so.

Image courtesy of NOAA. Download image jpg, KB. In the Atlantic and Northeast Pacific, we use the term "hurricane" to describe severe storms with high-velocity winds that rotate around a central, low-pressure core.

Because it is the interaction of warm air and warm seawater that spawns these storms, they form over tropical oceans between about 5 and 20 degrees of latitude. At these latitudes, seawater is hot enough to give the storms strength and the rotation of the Earth makes them spin. If a tropical depression remains over warm waters and is not diminished by another storm system or sheared apart by upper-level winds, it can strengthen into a tropical storm or hurricane.

Land surfaces also collect heat from the sun, but they do not retain heat as well as water. Land surfaces also release less moisture into the atmosphere.