General April Weather

[David]

Most models really getting off the leash on the 12z for next weekend. GFS going a fujiwhara effect scenario with a major hit on the NI from the initial superior cold core low and significant polar feed upper trough in the mix. Still needs few more runs before locking in but the sea surface temp is supportive of a major synoptic scale Tasman cyclonic gyre ATM.

Wow, that is a change from when I checked GFS yesterday. And showing the unsettled conditions continuing into early May as well. One to watch!

Anticyclonic gloom here this morning... total overcast

[jamie]

GFS and Access showing some mighty falls Saturday Sunday for the north island. The euro is showing not as much but the blocking high holds the low over the NI and it suddenly deepens on Monday.

Certainly looks like something rough is coming but hard to say what and when.

[Cyclone Tracy]

EC latest on the 00Z run is launching a serious cold shot into the South Island on Saturday. That looks like snow to 300m if it comes off. UKmet and GFS not as aggressive but have it on the radar.

Tasman depression a little less certain. At 144 hours EC, GFS and CMC are fairly close with the low off the west coast of the NI but the UKmet, BoM and Icon still have the low well out in the Tasman. Jury out....

[NZstorm]

Saturdays front over the upper North Island still looking potentially active with a thunderstorm possibility.

[Chris W]

Tuesday into Wednesday are looking a shade cold for the eastern South Island after the weekend’s action, according to the BOM.

[NZ Thunderstorm Soc]

2 more pictures from last Saturday night off Rangitata Island

[NZ Thunderstorm Soc]

Interesting day here.
A rather cold day but with a strong NW Arch.
No wind, justs slight SW drift judging from burn-offs in paddocks.

[NZ Thunderstorm Soc]

A wet day here with a total of 128.4mm for today. A record

[NZ Thunderstorm Soc]

211mm here for April in which seemed, initially, to be a dryish month overall but this system came along and buggered things up.
172mm for last WE all up. No rain today despite the overcastness, although it drizzled here last this evening.

[Cyclone Tracy]

128mm for April, year to date 522mm. Mean daily temp was 17.5c, 1.4c above average. Overall mean daily temp so far this year is currently 2.35c above average.

[David]

Stats from Howick for April 2018:

Total rainfall 183mm
Mean temp 16.3C
Avg daily min 12.4C
Avg daily max 20.7C
Lowest temp 6.4C (12th)
Highest temp 24.3C (17th)

[Nev]

A high frequency of lows crossing NZ during April made for a wet, volatile month for most places.

Apr 2018 Climate Anomaly Maps ℅ NIWA.gif

Some very preliminary April 2018 figures for the main centres:

Code: Select all

Apr 2016 Average Temps, Rainfall, Sunshine and departures from 1981-2010 normals ℅ NIWA

Site                     T-max °C      T-min °C      T-mean °C     Rain mm      Sun hrs

Auckland, Mangere       20.9  +0.8    13.6  +1.2    17.3  +1.1    155  184%    145   90%
Auckland Aero           20.7  +0.7    13.7  +1.0    17.2  +0.9    155  183%
Tauranga Aero           20.7  +0.7    12.4  +1.1    16.6  +1.0    119   99%    n/a   n/a
Hamilton Aero           20.1  +0.2     9.8  +1.4    14.9  +0.7    102  117%
Hamilton, Ruakura       21.2  +1.3     9.5  +0.5    15.3  +0.8     95  114%    154   93%
Wellington, Kelburn     17.2  +0.6    11.3  +0.6    14.2  +0.5    112  132%    168  104%
Christchurch Aero       17.5  +0.1     5.9  -0.6    11.7  -0.2    118  267%    157   97%
Dunedin, Musselburgh    15.4  +0.1     8.1  -0.1    11.8  +0.1    155  304%    136  108%
Greymouth Aero          15.6  -1.1     8.7  -0.3    12.2  -0.8    247  127%    116   82%

Note that all MetService sites are missing a day's data around the 21st. Nevertheless, some notable rainfalls included well over 200mm around the western Bay of Plenty/Rotorua area, over 360mm in Westland towns and around 900mm at Milford Sound.

Edit: Amended Wellington's temp figures.

[RWood]

A high frequency of lows crossing NZ during April made for a wet, volatile month for most places.


Apr 2018 Climate Anomaly Maps ℅ NIWA.gif


Some very preliminary April 2018 figures for the main centres:

Code: Select all

Apr 2018 Average Temps, Rainfall, Sunshine and departures from 1981-2010 normals ℅ NIWA

Site                     T-max °C      T-min °C      T-mean °C     Rain mm      Sun hrs

Auckland, Mangere       20.9  +0.8    13.6  +1.2    17.3  +1.1    155  184%    145   90%
Auckland Aero           20.7  +0.7    13.7  +1.0    17.2  +0.9    155  183%
Tauranga Aero           20.7  +0.7    12.4  +1.1    16.6  +1.0    119   99%    n/a  n/a
Hamilton Aero           20.1  +0.2     9.8  +1.4    14.9  +0.7    102  117%
Hamilton, Ruakura       21.2  +1.3     9.5  +0.5    15.3  +0.8     95  114%    154   93%
Wellington, Kelburn     16.6   0.0    10.9  +0.2    13.7  +0.0    112  132%    168  104%
Christchurch Aero       17.5  +0.1     5.9  -0.6    11.7  -0.2    118  267%    157   97%
Dunedin, Musselburgh    15.4  +0.1     8.1  -0.1    11.8  +0.1    155  304%    136  108%
Greymouth Aero          15.6  -1.1     8.7  -0.3    12.2  -0.8    247  127%    114   82%

Note that all MetService sites are missing a day's data around the 21st. Nevertheless, some notable rainfalls included well over 200mm around the western Bay of Plenty/Rotorua area, over 360mm in Westland towns and around 900mm at Milford Sound.

Meaning that the NIWA monthly stats. report - when it appears - will have missing mean/max/total values for temperature and rainfall for every single metService site that appears in the report?

[Nev]

Note that all MetService sites are missing a day's data around the 21st.

Meaning that the NIWA monthly stats. report - when it appears - will have missing mean/max/total values for temperature and rainfall for every single metService site that appears in the report?

Unless that data can be retrieved from on-site data-loggers (or manual observers), then presumably yes. Re the MS temps, NIWA's normal practice with missing data is to simply average by the remaining days. However, if that day(s) temps were extreme, this can throw the average out by a few points or more. I think using nearby proxy data (adjusted if need be) is far more accurate.

[RWood]

Meaning that the NIWA monthly stats. report - when it appears - will have missing mean/max/total values for temperature and rainfall for every single metService site that appears in the report?

Unless that data can be retrieved from on-site data-loggers (or manual observers), then presumably yes. Re the MS temps, NIWA's normal practice with missing data is to simply average by the remaining days. However, if that day(s) temps were extreme, this can throw the average out by a few points or more. I think using nearby proxy data (adjusted if need be) is far more accurate.

Thanks Nev. Will be interesting to see how much effort is expended.

[Nev]

Oops! Have amended Wellington's temps on my original table, based on only 28 days of data...