By Steven Strouss

PHILADELPHIA (CBS) – As of 3 p.m. Thursday, the mercury climbed to 97 degrees in Philadelphia which makes it the hottest day of 2013. The city of Philadelphia has not been this hot since July 24, 2012. Philadelphia is in a five day heat wave and Friday will be day six as Heat Index values rise to around 105 degrees again.

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Since Sunday, Philadelphia has recorded a temperature of 91 degrees, and we have reached the 90 degrees mark 16 days in 2013 with a total of four heat waves including one during the month of May.

An oppressive high pressure system has remained over the region and will continue to pump in southerly heat and humidity through Saturday.

An Excessive Heat Warning remains in effect for Philadelphia and surrounding counties while the rest of the region is under a Heat Advisory.

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Philadelphia has not seen a heat wave lasting six days since early July 2012. That heat wave brought temperatures of 100 to the city, setting multiple records across the region and lasting eight days.

The record highs for July 18th and 19th were both set just last year when Philadelphia reached 100 degrees both days. This time, most areas are expected to fall just short of the records.

Strong thunderstorms are expected to break the heat this weekend as a cold front pushes through late Saturday. The storms may bring downpours, gusty wind, hail and frequent lightning. Behind the front, temperatures will be in the mid-80s for a few days with more comfortable humidity levels next week.

Excessive heat is extremely dangerous to those working in the sun or without air conditioning. Extra caution should be taken when doing outdoor work between 12 p.m. and 6 p.m., and strenuous activities should be moved to the morning or evening hours. Also, remember to stay hydrated.

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