he National Weather Service in Chicago has issued a * Special Marine Warning for... Open Waters from Winthrop Harbor to Michigan City out to Mid Lake...Orange-shaded area on headlined map... * Until 145 AM CDT. * At 1207 AM CDT, a severe thunderstorm was located 15 nm northeast of Harrison-Dever Crib, moving northeast at 35 knots. Additional strong thunderstorms were occurring across the open waters offshore of Illinois, also moving northeast at 35 knots. HAZARD...Wind gusts to 40 knots and large hail. SOURCE...Radar indicated. IMPACT...Small craft could be damaged in briefly higher winds and suddenly higher waves. Large hail could result in structural damage. * The severe thunderstorm will remain over mainly open waters.