Recent observations depict a wind shift to northwesterly, accompanied by gusts to around 15 to 20 knots. These should be very sporadic in nature. Inexperienced mariners, especially those operating smaller vessels, should exercise caution if navigating the waters during this time.

* WHAT. Dangerously hot conditions with heat index values up to 110 expected. * WHERE. Southern Baltimore, Anne Arundel, St. Marys and Calvert Counties. * WHEN. From 11 AM this morning to 8 PM EDT this evening. * IMPACTS. Extreme heat and humidity will significantly increase the potential for heat related illnesses, particularly for those working or participating in outdoor activities.

* WHAT. Heat index values up to 105 expected. * WHERE. In Maryland, Carroll, Northern Baltimore, Northwest Montgomery, Northwest Howard and Northwest Harford Counties. In Virginia, Orange, Culpeper, Southern Fauquier, Eastern Loudoun and Northwest Prince William Counties. * WHEN. From 11 AM this morning to 8 PM EDT this evening. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur.

* WHAT. Heat index values up to 108 expected. * WHERE. Portions of central, northeast, northern and southern Maryland, The District of Columbia and central and northern Virginia. * WHEN. From 11 AM this morning to 8 PM EDT this evening. * IMPACTS. Hot temperatures and high humidity may cause heat illnesses to occur.

* WHAT. Heat index values around 100 degrees. * WHERE. Adams, Cumberland, Dauphin, Franklin, Lancaster, Lebanon, Perry, and York Counties. * WHEN. Until 8 PM EDT this evening. * IMPACTS. Hot and humid conditions may cause heat-related illnesses.