The term 'Marangai' means east wind, also meaning a storm, or bad weather. However, in some districts, Marangai means the north wind. It is likely that its meaning depended on the quarter from which bad weather tends to come in that district. Over the last week the upper North Island experienced an extreme weather sequence in what could only be called the Great Marangai. Sadly this weather sequence caused a loss of life, extensive property / infrastructure damage and countless landslides.
Here is the some of the important meteorological factors and timeline of events that took place.
Jan 21st – Joint Typhoon Warning Centre names Tropical cyclone 10P near New Caledonia. It only remained a cyclone for less than 1 day.
Jan 24th - The Australian weather model Access G starts to project 300mm+ rainfall event for Auckland and the Coromandel for the 26th/ 27th January. No other models looked this extreme but ultimately this would be an important hint of what was to come.
Jan 25th - Ex-tropical cyclone 10P connects with a mid-latitude trough which is dragging down large amounts of moisture from the tropics through an atmospheric river. Total precipitable water values have now increased to 50mm.
A new upper trough moves in from over the Tasman reinvigorating ex-tropical cyclone 10P.
Jan 26th - Ex-tropical cyclone 10P develops into deeper subtropical low with a rainband extending ahead of a warm front into Northland.
MetService issues widespread upper North Island 'Orange' heavy rain warnings.
Jan 27th - On sunrise, early signs of a significant rain event appear on water vapour images north of Northland.
King tide arrives across the Upper North Island
A significant convergence zone develops from lower Northland to southern Auckland from 2:00pm
Devastating and deadly flooding starts to appear in Auckland city, suburbs and roads as inundated storm water systems overload beyond capacity. 200 to 370mm was recorded in areas under the convergence zone.
1st severe thunderstorm warning was issued by MetService 4:18pm, 27th January.
MetService issues 1st RED warning for Auckland and Great Barrier Island at 9:07pm, 27th January. State of Emergency was issued by Auckland Council at 9:27pm. No emergency alert was sent by NZ Civil Defence for the day.
Jan 29th - A 2nd new upper level trough launches over the central Tasman, creating 2 new upper lows and a Fujiwhara effect.
Jan 30st - A large baroclinic leaf appeared along with a water vapour surge with equatorial origins. A consolidated upper low near Norfolk Island was in place to trigger the development of a surface low in the subtropics.
MetService issue a new Red warning for Northland, Auckland and the Coromandel
Jan 31st - Sunrise satellite imagery shows a new subtropical low with developing low-level Jetstream.
Wind gusts in the gulf clocked 64 knots 119 km/h the subtropical low deepened below 1000 hPa.
Feb 1st - A new convergence zone forms over the Gulf and moves over Auckland before sunrise. another 80 to 110mm falls on the city in only a couple of hours exacerbating and causing more flash flooding issues.
Feb 3rd - A final round of light to moderate rain fell across the upper North. Bringing to a close the most extreme rain event ever recorded in New Zealand's modern history for its most populated region.
Here are the final rainfall totals over 8 days from 27th January to 3rd February 2023 across the upper North Island recorded on private online gauges.
572 Hobsonville point
495 Mt Eden
467 Herne Bay
461 Auckland city
461 Beach Haven
458 Browns Bay
456 Mairangi Bay
453 Northcote Point
450 Campbells bay
439 Castor Bay
439 Murrays Bay
405 Gulf harbour
399 Stanmore Bay
399 Dairy Flat
398 Grey Lynn
377 Pataua North
370 St Heliers
366 Awhitu Peninsula
364 Coromandel town
359 Great Barrier Is
358 Kaipara Flats
344 Algies Bay
340 Mission Bay
315 Waiheke Island (Omiha)
311 Te Mata
293 Port Waikato
275 Waiheke Island (Onetangi)
237 Langs Beach
235 Bucklands beach
210 South Head
200 Waiheke Island (Matiatia)
Note: With heavy downpours, some localised large differences can occur between close gauges