4:46 p.m. update: The Maryland Department of the Environment has issued an air quality alert across Central Maryland for Wednesday, with "Code Orange" conditions. Code Orange indicates air pollution levels unhealthy for sensitive populations, including children, the elderly and those with certain health conditions such as asthma.
3:10 p.m. update: The heat advisory has been canceled, with lower than expected humidity in the air, but temperatures remain high in the mid-90s around the region. Heat index values were in the upper 90s to near 100 degrees Tuesday afternoon, with temperatures at 93 degrees at BWI and 96 degrees at the Inner Harbor about 3 p.m.
Original post, 1:39 p.m.: A heat advisory is in effect for Baltimore City and its surrounding suburbs between noon and 7 p.m. on Tuesday, with a heat index up to 105 degrees possible, according to the National Weather Service.
Such an index presents the potential for heat-related illness among the old and young and those without air conditioning, and officials across the region urged caution.
Temperatures will be in the upper 90s in the downtown area, and the lower 90s in the suburbs, on Tuesday afternoon, the weather service said. Temperatures reached 90 degrees at the Inner Harbor and 87 degrees at Baltimore-Washington International Thurgood Marshall Airport by 9 a.m.
By about 1 p.m., the heat index was at 98 degrees downtown and 94 degrees at BWI.
Local jurisdictions have opened cooling centers for those in need of a place to escape the heat. City pools will stay open two hours longer than normal because of the heat -- until 6 p.m. for neighborhood pools, dusk for most park pools and 8 p.m. for Druid Hill Park Pool.
Similar temperatures and high heat index levels are expected to last through the week. The 90-plus-degree heat wave will only taper off slightly on Sunday, when temperatures are expected to peak in the 80s, the weather service said.
Temperatures in the 90s have been relatively rare in 2013, compared with recent years.
Halfway through meteorological summer, there have been 10 days at BWI at or above 90 degrees so far this year, the second-lowest tally in the past five years, according to Foot's Forecast. However, Foot's points out, the summers of 2010, 2011 and 2012 were among the hottest on record here.
There have meanwhile been zero days to hit triple digits at BWI so far this year. The last was July 18, 2012.
The hottest temperature at BWI to date this year was Monday's high of 95 degrees, a relatively cool maximum compared with this point in recent years. The hottest temperatures before July 16 in recent years, according to Foot's Forecast:
2012: 104º on July 7th
2011: 100º on June 9th
2010: 105º on July 6th
2009: 91º on April 26th and 27th
2008: 96º on June 12th