When a tropical cyclone passes over cold water or land, the basic fuel, the warm sea water, is cut off. It removes storms source of moisture and heat. When it passes over land after landfall it weakens much. It is because of the loss of the warm moisture source.
A cyclone also weakens when it meets vertical wind shear. Wind Shear that is also called wind gradient is a difference in wind speed or direction over a short distance in the atmosphere. Low values of wind shear are needed to form a tropical cyclone. When major wind shear is present in the area, it interferes with the strengthening of the storm. Due to it the cyclone begins to weaken and die.
A tropical cyclone is like a heat engine that runs on warm, moist air. If dry, cool air moves into the storm, its presence reduces the deep convection that keeps the storm going. This can happen when the cyclone moves over cool water or land.
Sometimes a low pressure may develop above the storm in the higher regions of the atmosphere. This low pressure area above the storm causes inward flow above the storm. The rising air within the storm then has no escape and the storm collapses in on itself.
So, tropical cyclones dissipate when they can no longer extract sufficient energy from warm ocean water. As mentioned above, a tropical cyclone can contribute to its own death by stirring up deeper, cooler ocean waters. In addition, a cyclone that moves over land will abruptly lose its fuel source and quickly lose intensity.