perimeters of both the Gulf of Panama and the Golfo de Chiriquí, and wide mud flats extend up to 70 kilometers seaward from the coastlines. As a consequence, the tidal range is extreme. A variation of about 70 centimeters between high and low water on the Caribbean coast contrasts sharply with over 700 centimeters on the Pacific coast, and some 130 kilometers up the Río Tuira the range is still over 500 centimeters.
The country's two international borders, with Colombia and Costa Rica, have been clearly demarcated, and in the late 1980s there were no outstanding disputes. The country claims the seabed of the continental shelf, which has been defined by Panama to extend to the 500-meter submarine contour. In addition, a 1958 law asserts jurisdiction over 12 nautical miles from the coastlines, and in 1968 the government announced a claim to a 200 nautical mile Exclusive Economic Zone.
The dominant feature of the country's landform is the central spine of mountains and hills that forms the continental divide. The divide does not form part of the great mountain chains of North America, and only near the Colombian border are there highlands related to the Andean system of South America. The spine that forms the divide is the highly eroded arch of an uplift from the sea bottom, in which peaks were formed by volcanic intrusions.
The mountain range of the divide is called the Cordillera de Talamanca near the Costa Rican border. Farther east it becomes the Serranía de Tabasará, and the portion of it closer to the lower saddle of the isthmus, where the canal is located, is often called the Sierra de Veraguas. As a whole, the range between Costa Rica and the Canal is generally referred to by Panamanian geographers as the Cordillera Central.
The highest point in the country is the Volcán Barú (formerly known as the Volcán de Chiriquí), which rises to 11,401 ft. (3475 meters). The apex of a highland that includes the nation's richest soil, the Volcán Barú is still referred to as a volcano, although it has been inactive for millennia. Panama is also home to Balboa Hill, which offers a view of both the Pacific Ocean and the Atlantic Ocean.
Nearly 500 rivers lace Panama's rugged landscape. Mostly unnavigable, many originate as swift highland streams, meander in valleys, and form coastal deltas. The Kampia Lake and Madden Lake (filled with water from the Río Chagres) provide hydroelectricity for the area of the former Canal Zone. The Río Chepo, a major source of hydroelectric power, is one of the more than 300 rivers emptying into the Pacific. These Pacific-oriented rivers are longer and slower running than those of the Caribbean side. Their basins are also more extensive. One of the longest is the Río Tuira which flows into the Golfo de San Miguel and is the nation's only river navigable by larger vessels.
Panama has a tropical climate. Temperatures are uniformly high—as is the relative humidity—and there is little seasonal variation. Diurnal ranges are low; on a typical dry-season day in the capital city, the early morning minimum may be 24°C and the afternoon maximum 29°C. The temperature seldom exceeds 32°C for more than a short time. The humidity however, is around 80 percent for most of the year. Temperatures on the Pacific side of the isthmus are somewhat lower than on the Caribbean, and breezes tend to rise after dusk in most parts of the country. Temperatures are markedly cooler in the higher parts of the mountain ranges, and frosts occur in the Cordillera de Talamanca in western Panama.
Climatic regions are determined less on the basis of temperature than on rainfall, which varies regionally from less than 1.3 to more than 3 meters per year. Almost all of the rain falls during the rainy season, which is usually from April to December, but varies in length from seven to nine months. The cycle of rainfall is determined primarily by two factors: Moisture from the Caribbean, which is transported by north and northeast winds prevailing during most of the year, and the continental divide, which acts as a rainshield for the Pacific lo