With highs expected to flirt with 100 degrees for a second day in a row, one of the oldest records on the books for Baltimore could be challenged.

The highest temperature recorded on this date in Baltimore was 102 degrees, set in 1887. The record books go back to 1871. It's the oldest July high temperature record still standing in Baltimore, former weather blogger Frank Roylance pointed out.

Where that temperature was recorded is difficult to learn. Official weather observations for Baltimore were taken at the U.S. Custom House from 1893 until 1950, when Friendship Airport opened. Before that, observations were made from various city buildings over the years.

If temperatures reach 102 at the airport, now of course known as BWI Marshall, it will be the second high temperature record set this month. July 8, the high of 100 tied the old record.

Tuesday's high of 100 was one degree off of the record for that date, set in 1988.

A heat advisory is in effect across Central Maryland from 11 a.m. to 9 p.m., with heat index values expected to top 105 degrees. Cooling centers across the region are open, and residents are encouraged to check on elderly or infirm neighbors and relatives.

Heat has contributed to the deaths of three people since the earlier deadly heat wave ended July 8. Twenty-three people have died of heat-related causes in Maryland so far this month.

Have a weather question? E-mail me at sdance@baltsun.com or tweet to @MdWeather.