(Portland, OR)  --  Multnomah County and the City of Portland have issued emergency declarations ahead of this week's hot weather.  The National Weather Service has issued an Excessive Heat Watch from Monday through Friday, warning of dangerously hot conditions that could exceed 100 degrees for three or more days in a row.  Overnight lows will be in the mid to upper 60s.  The city and county will have overnight cooling shelters starting on Tuesday and some library branches will be open later than usual.  211 will have information on cooling centers.  TriMet will provide free transportation to cooling centers.