Hot spell (4,4)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">hot spell</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for heat wave that I've seen before include "Prolonged period of sunshine" , "Period of unusually warm weather" , "Long spell of hot weather" , "Continuous spell of hot weather" , "Period of unusuall hot weather" .)
(Another definition for winning streak that I've seen is " Successful run".)