The outside of the heated column cools, so water vapour condenses, forming a slightly conical cloud.  Inside that cloud wall, the rest of the heated column is still rising.  It is basically a pump lifting water from sea level to the top of the troposphere.
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As with any vapour cycle engine, evaporation is fastest at the highest temp., and condensation is fastest at the coldest temp.  The bigger the temperature difference, the faster the pump works.
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Air at 40C can hold more than twice as much water as air at 25C.  Water at 40C is more than twice as ready to evaporate as at 25C.
At the top, the condensed water is thrown out radially.
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If the input water temperature and sea-level air temperature are high, and the bottom-to-top temp. difference is big, the pump works really hard.  The harder it pumps, the lower the pressure at the bottom, which sucks in more moister air, faster.
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Irma was a big pump:
near record low pressure at sea level,
near record low temperature at high altitude.