The Metservice has issued a heavy rainfall warning for both western Tasman ranges and eastern hills of Richmond and Nelson.
The period of rainfall covers much of tomorrow (Wednesday 4th June), from 6am through to midnight.
The accumulated total of up to 150mm for western Tasman and 100mm for Richmond ranges are not overly high so would expect only moderate flows in larger river catchments.
However the intensities of up to 30mm/hr and the noted likelihood of possible thunderstorms could lead to heavy localised flooding in any areas these may occur.
For the major river catchments of Golden Bay (Aorere and Tākaka) would be expecting flows at around an annual flood level – this would cover most berm areas of these rivers.
On the Richmond Range side again annual flood flows are indicted for major rivers such as the Maitai and Wairoa/Waimea catchments.
There is some indication that rivers in the Upper Motueka (Motueka and Motupiko) may also experience flood flows at an annual flow or slightly above. But this is not likely to extend further down into the lower Motueka catchment.
Current forecast has the highest intensity rain during the afternoon, earlier in Golden Bay, later in Richmond/Nelson, and then corresponding flow peaks at the lower end of major rivers during the evening.
High Tide for Nelson on Wednesday is at 4:20 pm at a height of 3.4m.
This is a low high tide but timing is likely to coincide with potential peak rainfall which may exacerbate drainage issues around the coast.
It will also coincide with periods of stronger northerly winds which may cause increased coastal wave action to areas exposed to the north, such as Ruby Bay through to the Glen in Tasman Bay.
However the atmospheric pressure is relatively high for this event so actual coastal inundation/storm surge risk is very low.
Overall not a massive rainfall event but with any forecast like this should be planning for the impacts of some of these short sharp downpours as they may occur anywhere in these areas during this time period.
Keep up to date with the latest MetService warnings here(external link).