The National Weather Service has issued an excessive heat watch 36 hours ahead of what could be the start of a days-long stretch of temperatures nearing or above 100 degrees.The watch includes Howard, Anne Arundel and southern Baltimore counties and Baltimore City. It is in effect Friday morning through Friday evening.It warns of temperatures in the upper 90s to around 100 degrees and heat indices up to 110 degrees. The latest weather service forecast for Baltimore calls for a high of 102 degrees Friday.Such heat brings a risk of heat exhaustion, heat stroke and other heat-related illnesses, the weather service cautions.Friday's heat could come in a stretch of four or more days in the 90s, with a high of 95 expected on Thursday, 102 on Saturday, 99 on Sunday and 97 on Monday.Several of those days could threaten all-time heat records. One heat record has been tied this summer, with a high of 100 degrees June 21.Have a weather question? E-mail me at email@example.com or tweet to @MdWeather.