Tropical Cyclone Cody to bring large waves and potentially dangerous ocean conditions to New Zealand's coast
A new tropical cyclone that has been developing in the South Pacific Ocean is now officially named Tropical Cyclone Cody. It is currently situated southwest of Fiji. Forecast guidance has Tropical Cyclone Cody moving southeast during Wednesday and moving out of the tropics late Wednesday and Thursday. With wind speeds of 35 knots (65 km/h) within 110 km of its centre, Cody is currently classified as a Category 1 system but may intensify to a Category 2 or 3 system (Tropical Cyclone Activity - MetService New Zealand).
While the centre of the ex-tropical cyclone is currently forecast to track to the northeast of New Zealand, significant wave height along the northeast coast of New Zealand is expected to build rapidly from Friday the 14th and through the coming weekend. This means that some of the most popular summer holiday beaches in the North Island are forecasted to experience significant wave heights greater than 2-3 m by Sunday and peak periods jumping up to around 12 seconds. Larger waves can be expected at times (Figure 1), with infragravity or long-period surges possible at the coast (Figure 2). These conditions can potentially lead to hazardous swimming and land-based fishing activities along the northeast coast of New Zealand leading up to and over this coming weekend. The forecast comes after what has already been a challenging year for New Zealand with respect to drownings (News, Water Safety New Zealand).
While these events are still several days out, the forecast beyond the end of this week, is pointing to the remnants of Tropical Cyclone Cody potentially impacting the east coast of the North Island, with MetService and MetOcean Solutions actively tracking and reporting on the potential impacts of the event as it develops.
Figure 1. Whangamata marine condition forecast from SwellMap
Figure 3. Prototype of the rip current warning system being developed at MetOcean Solutions illustrating the outlook for the upcoming TC Cody in popular beaches around the North Island.
MetOcean Physical Oceanographer, Dr Rafael Soutelino, has developed New Zealand’s first national rip current warning system which is soon to be released on MetOcean Solutions’ recreational forecast site Swellmap. “The warning capability, which is based on developments at US National Ocean and Atmospheric Administration (NOAA; see also Dusek & Seim 2013) shows that the potential for rip generation increases dramatically from Friday at some of the most populated beaches along the NE coast of NZ” warns Dr Soutelino.
Consistent with how NOAA has implemented the system, a “red” warning colour indicates an exposed region or period with a greater than 50% chance of encountering a rip current of sufficient strength that would be dangerous to the average swimmer, while a “green” forecast indicates a region or period where the probability of encountering a hazardous rip current is lower (see NOAA national weather service).
“We’re looking forward to releasing this capability in New Zealand and to be providing both beachgoers and authorities with valuable information on the likelihood of hazardous rips occurring at New Zealand’s beaches. However, it's important to note that this capability does not replace common sense and the advice of the likes of Surf Life Lifesaving NZ but is intended to complement these services,” explains Dr Brett Beamsley, General Manager, MetOcean Solutions. “We’re also looking at the possibility to develop a similar capability for land-based or rock fishing” adds Dr Beamsley.
Figure 4. Cape Reinga Marine Heat Wave forecast issued 11th January 2022 (Moana Project)
In addition to the potentially hazardous conditions along the northeast coast of New Zealand, the ex-tropical cyclone is also expected to lessen the intensity of the marine heatwaves (MHW) that are currently taking place off Cape Reinga (e.g., Figure 4), Hauraki Gulf and the Bay of Plenty (moanaproject.org). The increased wave and wind energy induce vertical mixing of the ocean layers, which is likely to lower the sea temperatures. This relative cooling of the ocean surface is present in the Moana Project’s MHW forecasts for the whole of the north and east coasts of the North Island of New Zealand and could be strong enough to end the MHW event in the Hauraki Gulf. The exact mechanisms responsible for these MHW are being studied as part of the Moana Project (an MBIE Endeavour funded research project).