Hurricanes may lose strength over land because of cool temperatures, a lack of moisture, and/or friction.

Hurricanes form over low pressure regions with warm temperatures over large bodies of water. The warm temperature causes the ocean water to evaporate. The moisture is what fuels a hurricane. As the hurricane moves over land, the hurricane is no longer fueled by this moisture. Therefore, the hurricane begins to slow down and die as it moves further inland.

Secondly, hurricanes experience more friction over land than over the ocean water. This also slows down hurricanes.

Hurricanes do not only dissipate over land. Cool waters and strong winds may also decrease the strength of a hurricane.  A hurricane will begin to dissipate over cooler waters because cooler waters do not evaporate as much and, therefore, provide less moisture. Hurricanes need light winds at high levels in the atmosphere. A hurricane may be ripped apart by strong winds at high levels.

Why do hurricanes lose power once they reach land?

Hurricanes use the warm and moist water of the ocean as fuel. The warm air rises up and away from the surface leaving less near the surface (low air pressure). This is why they have more energy over the ocean than they do over land. They may be incredibly powerful over land but eventually they begin to die out. The warm ocean water is a necessity for the storm to grow.

Another reason that hurricanes lose power when they move over land is because of friction.

In addition, if the hurricane experiences vertical wind shear it will also lose its power.

Why do hurricanes lose power once they reach land?

Because storms draw their power and strength from the water they form over.  In shallow waters like the Gulf of Mexico, the surface temperatures tend to be warmer, which can cause the growth of superstorms like Hurricanes Katrina and Rita.  We all remember the amazing amounts of damage these two storms were able to do, yet once they made landfall, they rapidly lost strength and fizzled out.

Think of the large bodies of water, especially warm water, as food for hurricanes - more evaporation, more precipitation, and more wind speed.  Once on land there is nothing for them to continue to draw energy from, and the storm moves north and loses strength.

Why do hurricanes lose intensity?

Hurricanes are fueled by warm moisture. They form over warm ocean water in tropical regions. They lose intensity as they move over cooler water and as they move over land, where there is little moisture and buildings and landforms act as obstacles.

Water has a high heat capacity, or ability to store heat. This stored heat is called "latent heat", which means "hidden".When ocean water evaporates it contains more heat than it did as a liquid. When it condenses this heat is released, creating convection currents in the surrounding air. The convection currents provide the air movement that keeps the hurricane going. As it looses heat through condensation it loses its source of sustained kinetic energy.