PHILADELPHIA (AP) - As thousands of delegates arrive in Philadelphia for the Democratic National Convention, it's not just politics they have to contend with - it's also the hot and sticky weather.

The heat wave that descended on the city is expected to peak today, the convention's first day, with temperatures possibly hitting 100 degrees, said Mitchell Gaines, a meteorologist with the National Weather Service in Mount Holly, New Jersey.Many parts of the United States are experiencing higher than normal temperatures - like most of the Midwest - but the Philadelphia area is slated to be the hardest hit in the Northeast. Other parts of the region, including New York City, are in heat advisories. And the higher temperatures have brought powerful thunderstorms to some New England states, rain knocking out power to tens of thousands of residents."It's fair to say that the vast majority of the nation has been experiencing above normal temperatures for the past week," said David Robinson, New Jersey state climatologist at Rutgers University.The dome of high pressure traps hot air and is the basis for the "critical high temperatures" the country has been experiencing the past week, Robinson said, even for being the warmest time of the year.Thunderstorms are common, but don't help much with drought conditions in the Northeast and out west. Particularly dry weather in areas like Massachusetts and New York have forced farmers to choose which crops they will water and which will just not survive the season."The Northeast is a little bit of a mixed bag, but the bottom line is that the conditions have deteriorated over the past several weeks to a couple of months," said Rich Tinker, a drought specialist at the National Oceanic and Atmospheric Administration.In Arizona, where temperatures hit 112 on Friday, a 12-year-old boy died after becoming ill after a hike.Along with the considerable amount of humidity, the heat index in the Philadelphia area could be pushed as high as 108 today, Gaines said. Highs in the mid- to upper-90s are expected each day through Wednesday."The multiple days of excessive heat will greatly affect those who are attending outdoor activities, especially events with large groups of people that are gathering in the direct sun," the weather service said. Officials warned that in urbanized areas such as Center City Philadelphia, even nighttime temperatures may not drop below 80, especially Monday night.To protect thousands of demonstrators expected during the July 25-28 DNC, Philadelphia officials said two medic tents and two "misting" tents would be set up and water would be distributed. Medics also would be assigned to take part in marches.Workers preparing for the convention and others in downtown Philadelphia on Saturday afternoon were trying to keep cool.