Houston is the fourth-largest city in the United States and the largest city within the state of Texas. The city covers an area of 600 square miles (1,600 km²) with a population over 5.7 million. Houston is the economic center of the Houston–Sugar Land–Baytown metropolitan area—the sixth-largest metropolitan area in the U.S. Houston's climate is classified as humid subtropical. Spring supercell thunderstorms sometimes bring tornados to the area. Prevailing winds bring heat across the continent from the deserts of Mexico and moisture from the Gulf of Mexico. Rated as a beta world city, Houston's economy has a broad industrial base in the energy, manufacturing, aeronautics, transportation, and health care sectors and is a leading center for building oilfield equipment. Due to Houston's highly diversified industrial sectors, its economy is thriving, inflation is low, and the standard-of-living is relatively high. The Port of Houston ranks first in the United States in international waterborne tonnage handled and second in total cargo tonnage handled. The city has a large and growing international community. It is home to many cultural institutions and exhibits—attracting more than 7 million visitors a year to the Houston Museum District. Houston has an active visual and performing arts scene in the Theater District and is one of few U.S. cities that offer year-round resident companies in all major performing arts.