Storm-tide red-alert days 2021

Storm-tide red alerts are the highest high tide (also known as king tides) dates that Emergency Managers and Coastal Hazard Managers should write in their diaries and keep an eye on adverse weather (low barometric pressure, onshore winds), river levels and sea conditions (waves and swell).

The dates below are averaged across New Zealand. See tide forecasts for specific locations.

The following table shows the 2021 dates of the highest high tide "red alert" dates, and the lowest high tide "carefree" dates. It also includes dates when the moon's orbit brings it closest to [perigee] and furthest from [apogee] the earth.

2021: Range of dates collated across New Zealand

Red-alert dates (highest high tides)

Carefree dates (lowest high tides)

(actual lunar perigee date)

(actual lunar apogee date)


12-14 January  (Jan 10)


23-24 January  (Jan 22)

31 January-01 February  (Feb 4)


20-22 February  (Feb 18)

28 Feb-04 March  (March 2)


21-23 March  (Mar 18)

29 March-02 April  (March 30)


20-21 April  (Apr 15)

27 April-01 May  (April 28)


25-30 May  (May 26)


24-28 June  (June 23)


23-25 July  (Jul 21)


31 August  (Aug 30)


29 September-2 October  (Sep 27)

6-10 October  (Oct 9)


28-30 October  (Oct 25)

5-11 November  (Nov 6)


4-9 December  (Dec 4)


Visual representation of this calendar:

2021 calendar of red alert high tide dates:

There is a printable version of the 2021 calendar available for download [PDF 111.89KB]. 

Regional red alert days

Red alert tide days are available for different regions throughout New Zealand. 

Further information

High perigean-spring tides, colloquially known as "king tides", peak 1–2 days after New or Full Moon when Moon is in its perigee (i.e., when it is closest to the Earth during its 27½ day elliptical circuit around the Earth), but dates of highest tides vary around New Zealand.

In 2021 the Moon's closest perigee occurs on Dec 4* and coincides 2 hrs before a New Moon, with the next closest on 26 May (Full Moon). The year's highest high tides will occur in the two perigean phases of February to May and September to December.

"Red-alert" dates cluster around very high tides (perigean-spring tides) that peak 1–2 days after New or Full Moon when Moon is in its perigee and "carefree" dates cluster around lower high tides after First or Third Quarter when Moon is close to its apogee. 

Times for perigee, apogee and New and Full Moon in UTC (add 12 hours for NZST). 


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Coastal Technician