One of the wettest Aprils on record

One of the wettest April’s on record for the upper North Island

Notable monthly April rainfall totals for the upper North Island as of 9am 30th April.

Coromandel Peninsula

1042mm - Pinnacles

788mm - Waitekauri River

460mm - Whitianga

279mm - Thames

Northland

870mm - Hukerenui

726mm - Waitangi

692mm – Whakapara

423mm - Whangarei

Auckland

425mm – Dome forest

337mm – Swanson

323mm – Mt Roskill

262mm – Auckland city

Gulf Islands

305mm - Great Barrier (Claris airport)

212mm – Waiheke (Omiha)

Sources: Council and private online gauges

The Hauraki Gulf during ex-tropical Cyclone Tam

What caused it? (for weather geeks)

An atmospheric sting in the tail of the outgoing weak La Nina event (NOAA declared Dec 24 to Mar 25) via the Walker Circulation and an ongoing MJO pulse over the Western Pacific. This meant more moisture as tropical easterlies fed a north-easterly subtropical airflow into the upper North with stubborn high pressure to the east of NZ, producing multiple heavy rain events including ex-tropical cyclone Tam.

Strong tropical easterlies present in the region during April

The MJO pulse remained anchored over the Western Pacific during April

A similar analogue event in the past was the 2016-2017 weak La Nina event which also produced multiple deluges in April 2017 with the remnants of ex-tropical cyclones Debbie and Cook.