Tropical Cyclone Outlook: November 2019-April 2020

Tropical Cyclone Outlook: November 2019-April 2020


kia ora with the official start of the tropical cyclone season and November NIWA in collaboration with New Zealand MetService and meteorological Forecasting organisations in the southwest Pacific have prepared a tropical cyclone outlook the outlook covers the period from November 2019 to April 2020 For this season, as a whole, we’re expecting nine to twelve named tropical cyclones. This is close to normal for the region Taking a look at the risk across the Pacific the Solomon Islands Tuvalu Samoa Niue Tonga American Samoa the southern Cook Islands and the Austral Islands are expected to have an elevated risk for a tropical cyclone Compared to a typical season now looking at the rest of the region The countries that are colored in green have a near normal risk But Wallis and Futuna has a normal or elevated risk for tropical cyclones during the upcoming season The Society Islands as can be seen by the blue shading on the map have a reduced risk this coming season and several Pacific Island nations are unlikely to encounter tropical cyclones, and they are shaded grey on the map that we see here On average at least 1 ex tropical cyclone passes near New Zealand each year for the coming season The risk is near normal as New Zealand is shaded in green Note that the names of the countries you see on screen could be impacted by two or more tropical cyclones during the upcoming season Significant rainfall damaging winds and coastal impacts can occur leading up to and during tropical cyclones This is a reminder that all communities should remain vigilant and follow forecast information provided by the National Meteorological Service When putting this outlook together We look at analogs or seasons with similar background climate conditions to present. Ben, as a key contributing author to the outlook Please talk me through some of the guidance that was used Thanks, Nava We identified four seasons that were similar to the year 2019-20 many of these seasons featured Severe tropical cyclones. So that is category three or higher. In fact every season that we identified had at least Several severe tropical cyclones. We’ve looked at El Nino Southern Oscillation That’s ENSO and we compare it those past years to the current year to see if there’s similarities what we noticed, Nava Is that this year ENSO neutral is likely for the first half of the coming cyclone season But the second half of the season could feature El Nino conditions developing in the Central Pacific and that’s Important as you will see here in just a minute as we go through the rest of the outlook Thanks Ben. So in addition to the analogs. We also have been increasingly looking at dynamical model guidance around the world There are global models that look out further and time it’s a kind of Additional tool in the tool chest that we’ve been using and I guess that’s what we’re looking at here right then exactly Yes, so we’re looking at rainfall as a difference from normal for the upcoming cyclone season We’re going to start off here in the month of November notice There’s a lot of brown shades indicating below normal rainfall in the Coral Sea some green shades above normal rainfall near Fiji and also toward Tonga, but as we go ahead in time December It’s a pretty similar theme to November the changes occur as we go into the new year. So that’s 2020 So let’s take it into January. Now. We see a lot of greens beginning to appear around Fiji. Especially east of the International Dateline That’s where we’re highlighting an above average risk as we go to the second half of the cyclone season notice New Zealand’s looking pretty dry here in January 2020 a lot of that cyclone activity in that part of the season may be going to the east however, as we go forward in time February We see those greens expand even more here out toward, Vanuatu and New Caledonia Notice this green area to the south of Fiji might be indicative of an enhanced South Pacific convergence zone. This could be an area Breeding ground potential for tropical cyclones as we go into the second half of the season So I guess the take home here is the second half of this tropical cyclone season could be particularly active. That’s right and that might be influenced by a developing El Nino in the Central Pacific during the late part of the season and rounding things off in April notice, there’s some strands of green coming down toward New Zealand from both the Coral Sea area and also to the north so perhaps New Zealand it’s in the early part of 2020 that we’ll have to really start to watch the tropics to the north we also look at something called velocity potential, velocity potential is Something that we look at for identifying areas of rising and sinking motion around the earth, especially in the global tropics So pinks here showing sinking air and blues rising air. Exactly and this is for the December through February period so a lot of these blue shades that you see across the Central Pacific that could be Influenced by potential El Nino patterns during the second half of the upcoming season in the central part of the Pacific Those rainfall maps. We just showed you they have a similar spatial setup to this map So that lift that we’re seeing in the Central Pacific could help to encourage the development of tropical cyclones during the second half of the season and just As a recap the tropical cyclone risk for the coming season is displayed on the map Even though tropical cyclone activity is expected to be relatively low for some countries historical cyclone tracks indicate that tropical cyclones can affect all parts of the southwest Pacific region as With most years activity is expected to increase during the late part of the season from February through to April NIWA will continue to track the progression of the El Nino Southern Oscillation And update this guidance in January if needed if you’d like to read the full tropical cyclone outlook Please visit niwa.co.nz. thank you for joining us

Author: Kennedi Daugherty

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