The Enterprise BROCKTON — After four weeks in the "yellow," at moderate risk for COVID-19, Brockton will again be elevated to the highest risk category and into the "red" on Thursday. When the Massachusetts Department of Public Health releases its Weekly Public Health Report on Thursday evening, Brockton is expected to have had about 28.2 cases per day per 100,000 residents and a 4.21 percent test positivity rate from March 14 to 27, according to Dr. Richard Herman, the city's pandemic consultant. Communities that have more than 50,000 residents, which Brockton does, have to have both a test positivity rate over 4 percent and more than 10 cases per day per 100,000 people over two weeks to be in the high-risk "red."