New Zealand Weather Network

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TC Gretel

Introduction

A tropical depression is currently forming over  North Eastern Australia. This is expected to develop into a Tropical Cyclone over the next 48-72 hours, and if it does will be call TC Gretel.
 
As the video progresses you can see this depression develop into a TC, move  down across Norfolk Island, and onto or around Auckland as an ex TC. This is is expected to occur over the next week or so. Typically predicting TC tracks over this sort of timeframe is difficult due to uncertainties in weather patterns. However in this case, a number of forecast models, including ECMWF and GFS show a fairly tight cyclone track, so it can be assumed that the longer term prediction is more accurate than usual.
We'll be watching this one with interest over the next few days!
 
 
The spaghetti model issued Wednesday 11th March is provided below
 TC Track
 
The BOM Storm Risk statement for the area is as follows:
IDQ10810
Australian Government Bureau of Meteorology
Queensland

Tropical Cyclone Outlook for Coral Sea
Issued at 2:30 pm EST on Wednesday 11 March 2020
for the period until midnight EST Saturday 14 March 2020.

Existing Cyclones in the  Eastern Region:

Nil.

Potential Cyclones:  

There currently are no significant tropical lows in the Coral Sea. A weak
tropical low is currently over the Cape York Peninsula. This low is expected to
move eastward into the Coral Sea this evening and tomorrow, where it is
forecast to develop further. The low is expected to develop into a tropical
cyclone late in the week.

At this stage, the system is forecast to move to the east southeast while
remaining offshore of the Queensland coast. While the system is forecast to
remain offshore, strong to gale force winds are expected to occur in the
northern and central coastal waters before the system moves away.

A severe weather warning is current for heavy rainfall and damaging wind gusts.
For warnings: https://www.bom.gov.au/qld/warnings/

Likelihood of a tropical cyclone in the Eastern Region on:
Thursday        Moderate   
Friday          High       
Saturday        High       



NOTES: The likelihood is an estimate of the chance of each system being a
tropical cyclone in the Region for each day.
Very Low:     less than 5%                 Moderate:     20 to 50%
Low:          5% to 20%                    High:         over  50%

The area of coverage for this outlook is the Coral Sea and northern Tasman Sea
west of 160E.


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 Sunday 15th March 2020 1900

TC Gretel officially formed and was named this morning around 4:30am New Zealand Daylight time. Interestingly enough it was named by the Australian Bureau of Meteorology (BOM), but has since (by 4:30pm NZDT) moved out of their area of jurisdiction, and into that of the Meteorological Service of Fiji. TC Gretel is currently a Cat 1 cyclone (has mean winds 34-47 knots with a central pressure greater than 985 hPa).
The video below shows the last 40+ hours (time period Midnight 14 March to 1800 15th March) including the transition from tropical depression to tropical cyclone.
As you can see, some cloud is already impacting the top of the North Island, however as the cyclone has tracked further north than initially thought it is now unlikely to make a direct hit on the NZ mainland.
The latest statement from the Meteorological Service of Fiji, follows, along with the currently predicted tracker.
TCTrack1503200240UTC
 
 TROPICAL DISTURBANCE ADVISORY NUMBER A1 ISSUED FROM RSMC NADI Mar 150349 UTC. TROPICAL CYCLONE GRETEL CENTRE 988HPA WAS LOCATED NEAR 20.0S 161.0E AT 150000 UTC. POSITION POOR BASED ON HR HIMAWARI-8 VIS/EIR IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING SOUTHEAST AT ABOUT 17 KNOTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE ESTIMATED AT ABOUT 45 KNOTS. EXPECT WINDS OVER 33 KNOTS WITHIN 180 NAUTICAL MILES IN NE QUADRANT AND WITHIN 120 NAUTICAL MILES IN SE QUADRANT AND WITHIN 120 NAUTICAL MILES IN SW QUADRANT AND WITHIN 90 NAUTICAL MILES IN NW QUADRANT DEEP CONVECTION WRAPPING ONTO SUPPOSED LLCC WITH OVERALL ORGANISATION IMPROVING. OUTFLOW IS GOOD IN ALL CHANNELS. SYSTEM LIES IN A LOW SHEARED ENVIRONMENT WITH GOOD UPPER DIVERGENCE. CYCLONIC CIRCULATION EXTENDS UP TO 500HPA. SST AROUND 29 DEGREES CELSIUS. GRETEL IS CURRENTLY BEING STEERED TO THE SOUTHEAST BY THE SOUTHERN PERIPRHERY OF THE SUBTROPICAL RIDGE LOCATED TO THE NORTHEAST OF THE SYSTEM. DVORAK ANALYSIS BASED ON 0.65 WRAP ON LOG10 SPIRAL YIELDS A DT OF 3.0. MET=4.0 AND PT=3.5. FT BASED ON PT THUS YIELDING T3.5/3.5/D1.0/24HRS. FORECASTS : AT 12 HRS VALID AT 151200 UTC 22.8S 164.3E MOV SE AT 21 KT WITH 55 KT CLOSE TO CENTRE AT 24 HRS VALID AT 160000 UTC 26.1S 167.9E MOV SE AT 22 KT WITH 60 KT CLOSE TO CENTRE OUTLOOK : AT 36 HRS VALID AT 161200 UTC 28.8S 171.7E MOV SE AT 22 KT WITH 55 KT CLOSE TO CENTRE AT 48 HRS VALID AT 170000 UTC 30.6S 175.6E MOV SE AT 21 KT WITH 50 KT CLOSE TO CENTRE
 The spaghetti model from cyclocane.com is provided below
Spaghetti1503200240UTC

Monday 16th March 2020 

Around 1pm today TC Gretel moved past 25 degrees south, thereby moving out of the Fiji Meteorological Services responsibility and into the responsibility area for New Zealand's MetService. Currently the storm is at category 2. The last 24 hours tracking is provided in the video below:
 
The latest cyclone track map is below, issues by the Metservice
TCTrack1603200600UTC
 
The associated bulletin follows:
TROPICAL CYCLONE POTENTIAL BULLETIN ISSUED BY METEOROLOGICAL SERVICE OF NEW ZEALAND AT 2218 UTC 15-Mar-2020

CURRENT STATUS OF CYCLONE ACTIVITY

Tropical Cyclone GRETEL (980hPa) was located near 25.0S 168.1E at
151800UTC (7am Monday New Zealand time), or about 300km southeast of
Noumea New Caledonia, moving southeast at 28 knots. Maximum winds of
55kt (100km/h) near the centre.

FORECAST TO 1200 UTC TUE 17-MAR-2020
On its curent forecast track, TC GRETEL is expected to remain
offshore northern New Zealand, and continue moving east-southeast
while gradually weakening.

OUTLOOK UNTIL 1200 UTC FRI 20-MAR-2020
No other tropical cyclones are expected.
The core of the cyclone travels well north of New Zealand. There are sever weather warnings out for the north and east of the upper North Island and the Marlborough Sounds. Further details on these are available on the Metservice website
Watches and warnings
 
A better representation of the expected impacts can be seen in the video below, based on information from the windy.com site:
In this view, you can see the high pressure over the Tasman sea pushing the TC above and to the east of New Zealand. As it moves through, it drags cooler air from the south, providing chillier temperatures and in many places strong winds.

Tuesday 17th March 2020 2100

TC Gretel has become an ex tropical low. Metservice have published the following bulletin:
TROPICAL CYCLONE POTENTIAL BULLETIN ISSUED BY METEOROLOGICAL SERVICE OF NEW ZEALAND AT 2251 UTC 16-Mar-2020

CURRENT STATUS OF CYCLONE ACTIVITY

Ex-tropical cyclone GRETEL was located near 31.2S 178.4E at 161800
UTC this morning (7am Tuesday New Zealand time), or about 550
kilometres northeast of Northland, moving southeast.

FORECAST TO 1200 UTC WED 18-MAR-2020
The convection associated with Ex-TC Gretel dissipated early this
morning, over the relatively cool seas to the northeast of New
Zealand. Hence the system is no longer a tropical cyclone and has
been reclassified as an extratropical low. Ex-TC Gretel is expected
to move southeast over waters to the north and east of New Zealand
over the next few days, while remaining a deep extratropical low.
No tropical cyclones are expected.

OUTLOOK UNTIL 1200 UTC SAT 21-MAR-2020
No tropical cyclones are expected.
The last 24 hours of the system can be viewed below:
 

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