Belize is located in northern Central America, bordered by Mexico on the north, Guatemala to the west and south and the Caribbean Sea to the east. Including its territorial waters in the Caribbean, Belize's geographic coordinates are 15º 53' to 18º 30' north latitude and 87º 15' to 89º 15' west longitude. Using an offshore territorial limit of 20 km. (12 miles), the national territory covers about 46,620 sq. km (18,000 sq. m.), of which 49% is land. Belize's land mass includes more than 1,000 tiny islands, known as cayes (pronounced ‘keys’), totaling about 690 sq. km (266 sq. m). However, there are about 1,540 sq. km. (595 sq. m.) of lagoons on the mainland, reducing effective land area to some 21,400 sq. km (8,263 sq. m). The average dimensions of the Belize rectangle are about 260 km (156 miles) north to south and 180 km (109 miles) east to west; the mainland has 280 km (168 miles) of coastline. The barrier reef, the second longest in the world and the longest in the northern hemisphere, extends 200 km (132 miles) from the Mexican border in the north to the Sapodilla Cayes in the south.The climate is subtropical, with temperatures ranging from 21º C in the cooler months of October to February to 32.2º C in the warmer months of May to September. The annual mean relative humidity is 81.8%, while total rainfall varies from 1,588 mm to 4,290 mm, annually. The average annual rainfall over the past 15 years is reported at 2006 mm. There are two distinct seasons: a rainy season, which normally commences in late May and lasts until November, and a dry season, which stretches from December to early May. Topographic variations throughout the country are responsible for major fluctuations in air temperature, humidity and rainfall.The northern half and eastern fringes of the southern half of the country comprise a plain of low relief. The Maya Mountains, 300-1,100 m in altitude, occupy the south-center and dominate much of the remainder of the country. They rise steeply to a maximum of 1,120 m at Victoria Peak in the Cockscomb Range, and then slope down to the Vaca Plateau in the west. The third major physiographic feature of the country comprises karst landscapes, sometimes hilly and sometimes rolling, on the north and west of the Maya mountains. Prominent discontinuous foothill ranges exist in the southern interior and comprise much of the hinterland of the southern Toledo District. Though Belize is a relatively low country, its river systems and many perennial streams supply most of its water needs. The country is well endowed with both surface water, and water stored in aquifers, as evidenced by the fact that wells can be drilled almost 7 anywhere in the country with the expectation of reaching water. The Land Information Center (LIC) has identified thirty-two watersheds, although the National Hydrological Services classifies twenty-two major watersheds for Belize. Streams draining the southeastern and eastern slopes of the Maya Mountains have well-developed branching patterns with relatively steep, straight courses in the mountainous areas. On the coastal plain, streams become progressively more sluggish and drainage is less effective. Near the submerging coast, there are numerous lagoons, mangrove swamps, deep estuaries and river-mouth bars.