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The animated OPERA radar below shows no clear evidence of any orographic triggering or enhancement of the rainfall rates. Instead there are several examples of quasi-stationary triggering points over the ocean, which are probably maintained, temporarily, by back-building (where convective outflow meets inflow, gives convergence, which fuels more convection). These seem to have fed the prolonged extreme rainfall rates in the afflicted area. There was evidence on satellite imagery of a very similar process in and around the all-time-record Hawaii rainfall event (>1000mm in 24h) earlier in 2018. It would be good to uncover what aspects of an atmospheric vertical profile can be conducive to such back-building.
3. Predictability
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