I spent last week on Jeju Island, South Korea, for the Eighth International Workshop on Tropical Cyclones (IWTC-VIII) organized by the World Meteorological Organization (WMO). Every four years, the WMO convenes this meeting, which gets together forecasters and researchers from all over the world to review the last four years’ advances in the science of tropical cyclones (also known as hurricanes, typhoons etc.). It’s an invitation-only meeting, which reflects (or maybe is one of the causes of) the fact that tropical cyclone experts are a close-knit club. I had never been invited before, which I took to mean that I was not really part of the club. I guess I am now.
View east along the south coast of Jeju Island, near Jungmun Beach. In the foreground are basalt columns formed by rapid cooling of lava.
In the months before the meeting, the scientists involved put together a report to the WMO summarizing the advances since the last meeting in both basic science and operational forecasting practices. The structure of the meeting reflects the structure of the report. There are five overarching topics, each of which is a chapter, and a session of the meeting: 1. Motion; 2. Cyclogenesis, intensity and intensity change; 3. Communication and effective warning systems; 4. Structure and structure change; 5. Beyond synoptic timescales. Each topic has multiple subtopics, each subtopic has a “rapporteur” (or sometimes two) who led a team of people in the writing of their part of the report; the overall topic has a “topic chair” who organizes all of the subtopic reports and writes an introduction to the whole chapter.
I was the topic chair for topic 5, “Beyond synoptic time scales”. The word “synoptic” here refers to the time scale of a typical tropical cyclone forecast, a few days. The subtopics were climate change, seasonal forecasting, and intraseasonal forecasting – in that order, decreasing the time horizon sequentially.Seasonal forecasts are forecasts of overall tropical cyclone activity (with no details about specific storms on specific dates) for a particular region, made months in advance. The most important phenomenon that controls TCs on this time scale and makes the forecasts possible is El Nino. The “intraseasonal” time scale, also known as “subseasonal”, covers everything shorter than that, but longer than the range of a typical weather forecast. So, about 10 days to a month or two. On this time scale, the most important single phenomenon (though not the only one) modulating TC activity is the Madden-Julian oscillation, or MJO (see also here, here, and here).
Although I wasn’t at previous IWTCs, my sense is that at the last few, climate change has been a contentious topic. Around 2005, Katrina and the hyperactive Atlantic season of that year, combined with a couple of high-profile papers showing increasing trends in various measures of TC activity, caused a dramatic increase in the volume of research being done on the links between climate and TCs (and in the number of researchers doing it). Combined with some historical cultural differences between TC experts and climate scientists, this led to some growing pains in the field in the mid-late 2000s. A lot of that has been sorted out now. Not that we know everything or that everyone agrees on the fundamentals – far from it – but the field has advanced rapidly in a decade, and a lot of the early contention has shaken out. It’s much clearer what we know and what we don’t. So this part of the meeting, and the report, while not without debate, was actually relatively placid.
In my view the most exciting new developments have been in the intraseasonal arena. Just a few years ago – certainly a decade ago – weather forecast models could not predict the MJO to save their lives. The best ones have become dramatically better at it, and now show skill in MJO prediction out to as long as 4 weeks’ lead time. Since the MJO influences tropical cyclones, this – combined with broader overall improvement in the models – makes new kinds of forecasts possible, well beyond the 5-day time frame of current tropical cyclone forecasts.
Forecasts in this range, let’s say a week to 2-3 weeks, are just barely starting to come into view. They exist still mostly in research mode, and are mostly not yet issued to the public. There are a few exceptions; an example is the NOAA CPC Global Tropics Hazards and Benefits Outlook, a “climate-like” product which defines large areas in which things could happen in the next two weeks. Other, more weather forecast – like products are clearly possible, such as long-range forecasts of the track and intensity of a specific storm that are produced several days before it has formed (currently, no agency issues public track and intensity forecasts for a tropical cyclone before it actually exists) – such forecasts would not be highly accurate, but could give some indication of a threat to a broad region ten, or even 15-20 days in advance. The science and technology now exist, since just recently, to issue products with some skill in this range. But forecasters are conservative. Before they’ll issue such products, they need time to understand how good or bad these forecasts are, and to learn how to communicate them effectively so that users of the forecasts grasp the uncertainties.
Typhoon Hagupit on December 4, 2014. Day-night visible image from the VIIRS sensor on the NPOESS satellite, from the CIRA TC web page.
Meanwhile, during the whole conference, Typhoon Hagupit was drawing closer to the Philippines. It was quite a fearsome storm at midweek, reaching Super Typhoon status. We had regular forecast briefings during the latter part of the conference, from the Japanese and Korean Meteorological Agencies. Thankfully the storm weakened quite a bit before landfall. Between that and better evacuations, it looks so far like it won’t be near the disaster that Haiyan was last year. But Hagpuit provided a constant vivid reminder, as one presenter said at the start of this talk, of “why we do this”.