Kochi: IMD has extended yellow alert for heavy rainfall in the state till Thursday with a warning for thunderstorm accompanied by lightning and gusty winds at one or two places. Meanwhile, southwest monsoon is expected to reach Kerala by May 26 (Tuesday).On Sunday, all districts, except Palakkad and Wayanad, were on yellow alert. Ernakulam was on orange alert after receiving widespread rainfall. Except Kasaragod, Kannur, Palakkad, Kollam and Thiruvananthapuram, there will be yellow alert in all districts on Monday.Squally weather with wind speed 40-50kmph, gusting to 60kmph, is likely to prevail along and off Kerala coast till Thursday. Meanwhile, the state recorded 26cm rainfall between March 1 and May 24 against the normal of 28cm during the period, with a departure of 8% deficiency. Ernakulam, Idukki, Malappuram and Palakkad recorded deficient rainfall of 22% to 38% during the period. The highest rainfall on Sunday was recorded at Mattancherry with 8cm rain till 5pm, followed by 6cm rain at Ayyankunnu in Kannur.