WORLD METEOROLOGICAL ORGANIZATION ________________________________________

RA V/TCC-16 (29.VIII.2016) ___________________

RA V TROPICAL CYCLONE COMMITTEE FOR THE SOUTH PACIFIC AND THE SOUTH-EAST INDIAN OCEAN SIXTEENTH SESSION HONIARA, SOLOMON ISLANDS 29 AUGUST-2 SEPTEMBER 2016

ENGLISH ONLY

TCWC WELLINGTON REVIEW OF THE 2014/15 AND 2015/16 CYCLONE SEASONS

1.

Introduction

TCWC Wellington (operating within the Meteorological Service of New Zealand Ltd, or MetService) is responsible for issuing forecasts and warnings on tropical cyclones and/or reclassified cyclones over the ocean area from 160ᵒ East to 120ᵒ West between 25ᵒ South and 40ᵒ South, also for the coastal waters and land areas of New Zealand. The TCWC role is carried out by RSMC Wellington Lead meteorologists who also perform the Severe Weather Forecasting and Disaster risk reduction Demonstration Project (SWFDDP) tasks including the twice daily production of South Pacific Guidance (SPG) charts for the tropical area from 150ᵒ East to 150ᵒ West between 5ᵒ North and 25ᵒ South. The SPG charts and guidance contain references to existing and potential tropical cyclone activity, as well as more detailed information about precipitation, wind and waves during the pre-formation phase of a tropical cyclone. They also highlight any interesting cyclonic areas beyond that covered by the RSMC Nadi TC Outlook. All this information is contained on MetConnect Pacific, the SWFDDP password protected website. During the 2014/15 cyclone season, set against a neutral to very weak El Niño bias, a total of four of the eight1 named tropical cyclones in the South Pacific and Coral Sea basins exited the tropics into the Wellington area of responsibility. Of these, Pam was the most intense and crossed 25ᵒ South near 171ᵒ East early on 15th March 2015 as a category 5 severe tropical cyclone. Pam then continued on a southeast track, was reclassified northeast of New Zealand at latitude 33.5ᵒ South, before passing close to the North Island on 16th March 2015 producing strong winds and heavy rain in the northeast of the country. For further comments, see section 2 below. During the 2015/16 cyclone season, set against a very strong El Niño that weakened late season, a total of four of the eight2 named tropical cyclones in the South Pacific and Coral Sea basins exited the tropics into the Wellington area of responsibility as either a named or significant reclassified tropical cyclone. While Winston 1 2

Niko, Ola, Marcia, Pam, Nathan, Reuben, Solo, Raquel Tuni, Ula, Victor, Winston, Tatiana, Yalo, Zena, Amos

Authored by: Chris Noble Manager, Specialist Weather Services

Page 1 of 10

TCWC Wellington, MetService

was the most destructive and deadly system in the South Pacific during the season, it was not the most intense cyclone that Wellington assumed responsibility for. Winston crossed 25ᵒ South as a category 1 system early on 24th February 2016 and was reclassified six hours later before moving west into the Brisbane area. Ula was the most intense system that Wellington assumed responsibility for as it crossed 25ᵒ South near 170ᵒ East overnight on 11th January 2016 as a category 3 severe tropical cyclone. For further comments, see section 3 below. In advance of every tropical cyclone passing from the Fiji area of responsibility into the Wellington area of responsibility, RSMC Nadi shares its Tropical Cyclone Analysis Worksheet with TCWC Wellington so that there is consistency both in the application of the Dvorak technique and in the statement of intensity.

2.

2014/15 Cyclone Season

During the 2014/15 season, eight systems were named in the South Pacific and Coral Sea basins by RSMC Nadi and TCWC Brisbane; Niko, Ola, Marcia, Pam, Nathan, Reuben, Solo, and the very late season Raquel. Of these, Niko, Ola, Pam and Reuben all crossed 25ᵒ South into the TCWC Wellington area of responsibility as shown in the cumulative track map below, with more detailed comments following.

Cumulative track map for tropical cyclones that moved into the Wellington area during the 2014/15 season. Positions plotted are a blend of RSMC Nadi “operational” tracks (north of 25ᵒ South) and TCWC Wellington “verification” tracks (south of 25ᵒ South).

Authored by: Chris Noble Manager, Specialist Weather Services

Page 2 of 10

TCWC Wellington, MetService

2.1

Tropical Cyclone Niko

Niko crossed 25ᵒ South between 1200-1800 UTC on 23rd January 2015 near 146ᵒ West in French Polynesia as a category 1 cyclone, and was reclassified at 0000 UTC on 24th January 2015 over open waters near 26.3ᵒ South 146.6ᵒ West after just one TC warning issue in the Wellington area.

2.2

Severe Tropical Cyclone Ola

Having earlier reached category 3 intensity, Ola crossed 25ᵒ South between 1800 UTC on 2nd February 2015 and 0000 UTC on 3rd February 2015 near 162ᵒ East to the southwest of New Caledonia as a category 2 cyclone. Ola then curved to the southeast and was reclassified the following calendar day at 1800 UTC on 3rd February 2015 near 30.5ᵒ South 164.3ᵒ East. The remnant low then continued on a southeast track towards the North Island of New Zealand, but its impact on the country was minimal. While expected conditions did not warrant public severe weather warnings, a period of brief heavy rain did affect the north of the country.

2.3

Severe Tropical Cyclone Pam

Pam, the most intense and destructive cyclone of the 2014/15 season in the South Pacific, crossed 25ᵒ South between 1200-1800 UTC on 14th March 2015 near 171ᵒ East to the southeast of New Caledonia as a category 5 severe tropical cyclone. After crossing into the Wellington area, Pam continued on a southeast track and slowly weakened, eventually undergoing extra-tropical transition and reclassification at 1200 UTC on 15th March 2015 near 33.5ᵒ South 178.7ᵒ East. At the time of reclassification, Pam was still a powerful extratropical system and was analysed with a central pressure of 965hPa and maximum winds of 70 knots. Pam’s closest approach to mainland New Zealand was at 0000 UTC on 16th March 2015 when it passed approximately 105 nautical miles offshore from East Cape in the North Island, still with a central pressure of 965hPa and maximum winds of 70 knots. Pam was analysed with hurricane force winds all the way to 45ᵒ South as it passed and moved east of the Chatham Islands.

2.3.1 Pam’s Impact on New Zealand On Monday 9th March 2015, shortly before TC Pam was named later that day, MetService meteorologists assessed a threat to New Zealand from an ex-tropical cyclone and began regular issues of both press releases3 and blog posts to keep the media and public up to date with the latest official advice from both RSMC Nadi and TCWC Wellington. By Wednesday 11th March 2015, two days before Pam crossed Vanuatu, the severe weather forecast team at MetService published a Severe Weather Outlook advising of the threat of both heavy rain and severe gales over the North Island of New Zealand (especially in the northeast) on Sunday 15th and Monday 16th March

3

First press release related to Pam: “Keeping an eye on the tropics” – 9th March 2015

Authored by: Chris Noble Manager, Specialist Weather Services

Page 3 of 10

TCWC Wellington, MetService

2015. On Thursday 12th March 2015, NWP guidance for the track of Pam was becoming more certain and the media team at MetSevice published a forecast track map showing the passage of Pam just northeast of the North Island. The first Severe Weather Watch for the event was issued on the morning on Friday 13th March 2015, highlighting the threat of heavy rain and severe gales from the night of Sunday 15th March 2015 in a number of provinces in the northeast of the North Island. An update later the same day highlighted the threat of dangerous wave conditions along eastern coasts of the North Island. The following day, during the morning of Saturday 14th March 2015, the first Severe Weather Warning was published (soon after Pam crossed southern Vanuatu) covering both heavy rain and severe gales in the northeast of the North Island. As Pam approached northern New Zealand, rain set in over the far north of the country during the morning of Sunday 15th March 2015 while winds over the upper North Island steadily increased. Heavy rain and strong winds then spread down the Island and continued into Monday 16th March 2015 as Pam tracked southeast past the North Island producing a lowest pressure of 974.7hPa at Hicks Bay near East Cape at midday.

ASCAT METOP-A ocean surface winds via NOAA for ex-TC Pam northeast of the North Island at 2140 UTC on 15 March 2015, shortly before closest approach to mainland New Zealand. Authored by: Chris Noble Manager, Specialist Weather Services

Page 4 of 10

TCWC Wellington, MetService

The largest rainfall accumulations occurred in northern parts of the Gisborne province in the northeast of the North Island where many weather stations recorded between 100-200mm in a 24 hour period, with a peak of 229.5mm in 24 hours4. Rainfall rates peaked at 23.5mm per hour5, and were generally between 10-20mm per hour at a number of stations, leading to slips and road closures. The strongest winds were recorded in Northland at the Kaeo radar site (elevated at 397m) where winds peaked with a mean speed of 61 knots and gusts of 80 knots (113 km/h gusting 148 km/h). Gusts of 78 knots (144 km/h) were recorded at Channel Island near Coromandel Peninsula northeast of Auckland and at Hicks Bay in Gisborne, with wind in both areas leading to power cuts due to downed trees and power lines. In addition to heavy rain and strong winds, very large seas inundated northeast coasts of the North Island breaching some sea walls and leading to evacuations of residents in coastal towns in Gisborne. Examples of coastal inundation are shown in the photos below, originally posted to Twitter;

“The scene at Te Araroa right now, 120km north of Gisborne. High tide is bringing waves and debris past the seawall.”- @jehancasinader, 3:48PM 16 Mar 2015

“The road along the East Cape of NZ after #CyclonePam #pam passed by”- @geoffmackley, 8:40PM 16 Mar 2015

Also on 16th March 2015, with Pam expected to track close to the Chatham Islands with hurricane force winds, a proactive “state of local emergency” was declared for the Islands by NZ’s Ministry of Civil Defence and Emergency Management (MCDEM)6. Pam eventually tracked northeast of the Chatham Islands, where a lowest pressure of 968.6hPa was recorded at 0200 UTC on 17th March 2015, after winds peaking six hours earlier at southeast 45 knots gusting 59 knots (83 km/h gusting 109 km/h). For further comments on cyclone Pam, see the MetService blog post: TC Pam Summary.

4

At Pouturu Bridge in Gisborne At both Te Puia and Pouturu Bridge in Gisborne 6 Announced by MCDEM on Twitter 5

Authored by: Chris Noble Manager, Specialist Weather Services

Page 5 of 10

TCWC Wellington, MetService

2.4

Tropical Cyclone Reuben

Reuben crossed 25ᵒ South between 0600-1200 UTC on 22nd March 2015 near 174ᵒ West to the south of Tonga as a category 1 cyclone, and was reclassified at 0000 UTC on 23rd March 2015 near 26ᵒ South 174ᵒ West.

3.

2015/16 Cyclone Season

During the 2015/16 season, eight systems were named in the South Pacific and Coral Sea basins by RSMC Nadi and TCWC Brisbane; Tuni, Ula, Victor, Winston, Tatiana, Yalo, Zena, and Amos. Of these, Ula and Winston crossed 25ᵒ South into the Wellington area of responsibility as named systems, while Victor crossed after being reclassified by RSMC Nadi. Additionally, Tatiana crossed 25ᵒ South near the boundary triple point on 160ᵒ East between RSMC Nadi, TCWC Brisbane and TCWC Wellington, but was handed over from RSMC Nadi to TCWC Brisbane. Tracks for these four systems are shown in the cumulative track map below with more detailed comments following.

Cumulative track map for tropical cyclones that moved into the Wellington area during the 2015/16 season. Positions plotted are a blend of RSMC Nadi and TCWC Brisbane “operational” tracks (north of 25ᵒ South) and TCWC Wellington “verification” tracks (south of 25ᵒ South).

Authored by: Chris Noble Manager, Specialist Weather Services

Page 6 of 10

TCWC Wellington, MetService

3.1

Severe Tropical Cyclone Ula

Ula was the most intense tropical cyclone of the season that TCWC Wellington assumed warning responsibility for as it crossed 25ᵒ South between 1200-1800 UTC on 11th January 2016 near 170ᵒ East to the southeast of New Caledonia as a category 3 severe tropical cyclone. Ula then continued on a southeast track and weakened, being reclassified at 1200 UTC on 12th January 2016 near 29ᵒ South 174ᵒ East. The remnant low continued moving east towards Raoul Island (located near 29.3ᵒ South 177.9ᵒ West, for which MetService provides a warning service), but recurved to the west prior to reaching 180ᵒ after which time it dissipated over open waters well north of New Zealand.

3.2

Severe Tropical Cyclone Victor

After earlier reaching category three status, Victor was reclassified at 1200 UTC on 22nd January 2016 around 50 nautical miles south of Nuku’alofa in Tonga. Victor then curved to the south and crossed 25ᵒ South into the Wellington area around 24 hours later, soon after 1200 UTC on 23rd January 2016. Despite reclassification, the system persisted as a significant extra-tropical depression and carried gale force winds (and marine high seas warnings) all the way to 40ᵒ South to the east of New Zealand. Ex-TC Victor’s closest approach to mainland New Zealand was on the morning of 28th January 2016 when it tracked southwards approximately 40 nautical miles offshore from East Cape in the North Island (see below for satellite and radar imagery of the system just east of the North Island).

3.2.1 Victor’s Impact on New Zealand On Saturday 23rd January 2016 (prior to ex-TC Victor crossing 25ᵒ South), the severe weather forecast team at MetService published a Severe Weather Outlook highlighting a risk of heavy rain in the east of the North Island on Wednesday 27th and Thursday 28th January 2016 due to the passage of the former cyclone. This advice was refined on Sunday 24th January 2016, with increased confidence for heavy rain in the Gisborne and Hawkes Bay provinces (in the northeast of the North Island), along with the potential for severe gales. On the morning of Wednesday 27th January 2016, the first Severe Weather Warning was issued for a period of heavy rain in the Gisborne province the following day. Later on Wednesday 27th January 2016, the Warning was expanded to include northern parts of Hawkes Bay and a Severe Weather Watch was issued for the possibility of severe southwest gales about the coast. On Thursday 28th January 2016, as ex-TC Victor passed just offshore, widespread heavy rain fell throughout the regions of Gisborne and northern Hawkes Bay. A number of weather stations recorded rainfall in excess of 100mm in just 12 hours, with a peak 12 hour accumulation of 154mm7. Hourly rainfall rates exceeded 20mm per hour across many stations, peaking at 30mm per hour8, resulting in several slips and washouts closing some 7 8

At Pukeorapa in northern Hawkes Bay At both Te Puia and Willow Flat in Gisborne

Authored by: Chris Noble Manager, Specialist Weather Services

Page 7 of 10

TCWC Wellington, MetService

roads in the Gisborne region. The peak wind gust recorded was 61 knots (113 km/h) at the Mahia Radar site, although the station there is elevated on a peninsula at 417m above sea level.

Ex-TC Victor passes just east of the North Island on 28th January 2016; true colour Himawari-8 image courtesy JMA valid 0230 UTC and radar image valid 0236 UTC.

3.3

Severe Tropical Cyclone Winston

Winston, the most intense, destructive and deadly cyclone in the South Pacific during the 2015/16 season, crossed the Wellington boundary on 25ᵒ South three times in its lifetime as a named cyclone. After passing east of New Caledonia on a southerly track early in its lifetime, Winston curved to the southeast and eventually northeast again, dipping below 25ᵒ South briefly – believed to be only the second time on record this has happened after TC Jasmine in 2012. While Winston was south of 25ᵒ South briefly as a category 3 Severe Tropical Cyclone (it earlier crossed as a category 4 system), RSMC Nadi retained warning responsibility for the three synoptic warning times from 0000-1200 UTC on 14th February 2016. This arrangement followed discussions between forecasters at Nadi and Wellington and was based on good agreement in models for a recurve to the north and back into the Nadi area – a pragmatic decision for warning responsibility given the forecast track. Winston again crossed 25ᵒ South around 10 days later at 1800 UTC on 24th February 2016 near 172.5ᵒ East to the southeast of New Caledonia as a category 1 system and was reclassified 6 hours later at 0000 UTC on 25th February 2016 near 26ᵒ South 171ᵒ East.

3.3.1 Co-ordination with RSMC Nadi During Friday 19th February 2016, as Winston settled on a westward track after recurving to northeast of Tonga, it become increasingly clear the system would affect Viti Levu over the following 24 to 48 hours with a Authored by: Chris Noble Manager, Specialist Weather Services

Page 8 of 10

TCWC Wellington, MetService

potential to disrupt communications due to a possible track over or near Suva (the subsequent track was farther north than early expectations). As a result, TCWC Wellington initiated preparations to provide back-up support for RSMC Nadi. As Winston approached the eastern most islands of Fiji (near the Lau Group) late morning on Saturday the 20th February 2016, TCWC Wellington and RSMC Nadi initiated a check bulletin procedure to monitor and confirm working communications to/from Fiji. Under this procedure, a “ping-pong” style approach for messaging is employed every 30 minutes, with check messages transmitted by RSMC Nadi and immediately acknowledged by TCWC Wellington in a return message. Failure of any check message to arrive triggers further communication checks, while failure of three consecutive check messages coupled with no other available communications with Fiji triggers full backup procedures in which TCWC Wellington assumes all RSMC Nadi responsibilities. During the overnight period and passage of Winston across the northern part of Viti Levu, communications remained functional and the duty TC forecaster in Wellington maintained contact with colleagues in Fiji both through check messages and direct phone calls. The check message procedure continued through to early afternoon on Sunday the 21st February 2016, by which time Winston had passed well to the west of Fiji. Relevant media and government agencies in New Zealand were also updated regularly during this time, including Radio New Zealand International and the Ministry of Foreign Affairs and Trade who, through their Pacific Division, coordinate the inter-agency Emergency Task Force whose role is to consider, plan and manage the New Zealand disaster response in the South Pacific.

3.4

Tropical Cyclone Tatiana

Tatiana was named over the Coral Sea by TCWC Brisbane just six hours after Winston was named east of Vanuatu by RSMC Nadi. Tatiana moved southwards close RSMC Nadi’s western boundary on 160ᵒ East during Saturday 13th February 2016, and crossed 25ᵒ South between 1200-1800 UTC the same day near the boundary triple point between RSMC Nadi, TCWC Brisbane and TCWC Wellington as a category 1 cyclone. Despite crossing into RSMC Nadi’s area of responsibility, TCWC Brisbane continued warnings on the system allowing RSMC Nadi to focus monitoring and warning resource on TC Winston. Tatiana was reclassified at 1800 UTC on 13th February 2016 near 25.6ᵒ South 160.0ᵒ East.

4.

Operational Track Verification

Verifications of analysis and 12/24 hour forecast positions for the 2014/15 and 2015/16 seasons show mean position errors have continued a downward trend based on a five-year moving average as demonstrated in the graph below. While the moving average trend is down across all time steps, there was a notable spike in the 12 hour mean error during the 2014/15 cyclone season. This was the result of two H+12 forecast positions for TC Ola based on a forecast movement that was too slow. In reality, Ola accelerated prior to extra-tropical transition and reclassification. The two warning issues did not contain H+24 hour forecast positions for verification, thus only the H+12 mean errors were affected.

Authored by: Chris Noble Manager, Specialist Weather Services

Page 9 of 10

TCWC Wellington, MetService

Graph of TCWC Wellington mean position errors for the analysis (H+00) and forecast (H+12 and H+24) position in operational TC warnings for the high seas. The 14 year period above includes 42 cyclones and 145 analysis (H+00) positions.

Mean position errors for named TC’s in the TCWC Wellington area of responsibility during the 2014/15 and 2015/16 cyclone seasons were; Season

Num. TC’s

Num. H+00 points

H+00 mean error

H+12 mean error

H+24 mean error

2014/15

4

8

22km

160km

73km

2015/16

2

5

5km

63km

93km

[end]

Authored by: Chris Noble Manager, Specialist Weather Services

Page 10 of 10

TCWC Wellington, MetService