Saturday could even challenge the July 7 record of 103, set two years ago, said Walter Drag, a meteorologist with the National Weather Service in Mount Holly. The key is whether cloud cover blocks the sun during the warming part of the morning into the afternoon.
The warmest temperature on record for Philadelphia was 106, set on Aug. 7, 1918.
Drag said Saturday could still be within the top three or four warmest days on record. Humidity is expected to be high, meaning the heat index could make it appear much hotter. An excessive heat warning is in effect through 8 p.m. Saturday. Thunderstorms are possible, although their strength is difficult to predict.
The longest heat wave on record for the region lasted 18 days in 1988. The current heat wave, which should end Sunday would be 11 days.
"We're presuming it ends Sunday," Drag said. "If not, it's a different ball game."
The forecast for Sunday calls for partly sunny with a chance of showers and thunderstorms and highs in the lower 90s.
Then, temperatures will dip a bit next week, with highs in the mid 80s predicted for Monday.
With an excessive an heat warning in effect, the Philadelphia Corporation for Aging (PCA) has activated its Heatline, 215-765-9040.
The Heatline call center will be in operation Thursday and Friday from 8:30 a.m. to midnight and 8:30 a.m. to 8 p.m. Saturday to answer questions from the public about heat related problems and how to cope.
City officials are urging neighbors, friends and relatives to check on elderly residents, who are particularly vulnerable to the heat.
The Pennsylvania Department of Environmental Protection also issued a warning for high ozone levels and said young children, the elderly and those with respiratory problems, such as asthma, emphysema and bronchitis, should limit outdoor activities.