Severe Tropical Cyclone EVAN (Samoa-Fiji)

[Chris Raine]

I have this one
NANDI in FIJI
Dec 17 04:00 22 min ago

SPECI SPECI NFFN 170400Z 05050G81KT 6000 +RA SCT023 SCT043 OVC100 24/24 Q0970
TEMPO 3000 +RA RMK RR 15.0=

which is 5pm local NZ time I think. Pressure has clicked up 2hpa

[Hordur]

they must be using the australian colour scheme...
how do you get red on the rain radar when a cat 4 TC is only green?

That image was showing rainfall rate in mm/hr, not reflectivity.

[Manukau heads obs]

yeah, I noticed that...still was not very high on the mm/hr scale either?

[Konstantinos]

So far, what is the chance Evan goes to New Zealand?

[Manukau heads obs]

still the same chance
but as been already stated, its just a low of tropical origin (i.e gales and heavy rain)
by the time it gets here
which side of the north island it goes down is the million dollar question, which will affect where the rain falls
and if it stalls near NZ and so keeps a humid NE flow onto the upper north island, meaning a humid and damp xmas period

[Konstantinos]

And about records, what is the biggest cyclone (about category) which has ever been in New Zealand (Auckland)? Tropical Storm or Category 1,2?

[Manukau heads obs]

there has never neen a "tropical cyclone" that has hit NZ
i.e they are always lows of tropical origin
however they are still refered to as ex tropical cyclone "name" or just cyclone "name" when they get here

as the sea temperatures are not warm enough to maintain a center of circular convection (CB's)

(except one a couple of years ago that maintained that structure right up to just off shore from the bay of islands, due to warmer than warmer sea temperatures north of NZ (23 to 24 C))

but these lows can under go extra tropical transition to an intense mid latitude depression if they encounter cold air (e.g a cold front)
that is what happened to the Waihini storm that hit Wellington

or the can deepen again if they tap into a cool but moist feed around a high pressure area..thats what happened with Bola (i.e the rainining out of the tropical moisture air mass by cooling leads to a drop in air pressure...and if that happens at the same time as a high is intensifying then you can a classic 'egg beater' situation)

[Konstantinos]

Ok, I understand, thank you.

Tropical Cyclone Evan Hammers Fiji

http://www.weather.com/news/weather-hur ... n-20121216

[Manukau heads obs]

Evan is doing alot of unravelling at the moment, spreading out...

[spike_01]

Hopeful it will go down the Eastern side, and be pretty much over by Christmas Day..

In saying that, I am of the opinion that Gisborne and surrounds will be hit pretty hard with flooding..

[Manukau heads obs]

seems to be weakening rapidly now, over the colder water
might not be anything left to come down this way ....
mind you, if it can tap into some of this cooler air mass that arrived with the new high pressure SW change
then it might help the extra tropical transition instead of just raining out to the north of us

[NZstorm]

Warm moist air moving south will generate rain (warm front effect).

There is still model variation on the movement of Ivan. If the gfs does verify looks like Gisborne will catch a lot of rain.

[Cook]

Not a very nice day up north, but perhaps they need the rain. From there it is expected to move southeast so Gisborne may not get much rain out of this.

evan.JPG

[Manukau heads obs]

the JTWC has it weakening rapidly (you can see it has been affected by wind shear badly and the LLCC is now fully exposed with convection only in the SE quarter)
and expects it to DISSIPATE in 48 hours

and since its been moving S and not SSW, if the remains keep moving S then only East cape is going to get the effects of it...if it keeps on moving south...the new replacement high pressure could block its path altogether....
will be interesting to see what comes of the remains...certainly lots of potential rain bearing humid air mass with it!

[Manukau heads obs]

in fact, it has moved slightly SE of S since leaving Fiji...and continues to do so...
it will need to re curve more SW if it is to impact the NI
sure would be a nice xmas present, the rain,for farmers/growers...

[spwill]

GFS has Gisborne/HawkesBay in line for the main rain while ECMWF has the low tracking a bit further west so Gisborne to Northland catching the heavy rain with that model. The GFS outcome is more likely to give Auckland a reasonable Xmas day while ECMWF suggest cloudy humid/ chance showers for Ak Xmas day .

[Manukau heads obs]

if anything its moving more SE at the moment..
edit: often though the upper level cloud can move SE (get sheard off), but the actual LLCC, i.e at the surface, will stay put....on its original path..
but that path will get blocked more as the replacement incoming high strengthens the high to the east
and so I guess it will swing down onto the north island
will all that moisture and onshore flows onto ranges,and if it becomes slow moving, potential for flooding type rain falls?

[jamie]

looks to be moving a long way east or is that just the cloud falling east off the low center like Brian suggests. To me it looks more than that.

[Manukau heads obs]

it was just the wind shear
you can see the low center now..its fully exposed...
its still in the same general place , south of Fiji...

[jamie]

Its hardly moving and i struggle to see it moving west unless it suddenly gets a move on. To me it still looks like a very very slow SSE movement at this stage.

[Manukau heads obs]

could be famous last words
LOL

[boomer]

Multi modelling has Evan swiping the top of the North Island before heading into the Tasman.
EC has been truly awful (as was with an earlier low in the South Pac) re Evan.
In my (often woeful) reckoning that ridge will, dependent on its strength, take it to the SE. Either way there will be a Chrissy present.

[Manukau heads obs]

overnight the patient has remained stable
just a very slow movement south

[boomer]

Evan's gone... dry and sheared
http://www.goes.noaa.gov/sohemi/sohemil ... wvgms.html

[boomer]

Perhaps not..... sorry... the space is there re the North Island
http://weather.uwyo.edu/cgi-bin/model?M ... sl&C2=pmsl