Talim making landfall in China; Whose forecast is it anyway?

TLDR: Atlantic – Don may become a tropical storm but is only of interest to fish and ships. East Pacific: Calvin is weakening but may brush Hawaii as a weak tropical storm in a few days. The real story is the impending landfall of Typhoon Talim in southern China today. Here’s the details, along with a discussion about who is responsible for forecasts around the world and why that matters …

Talim is now a full typhoon, and is already disrupting life across the southern coast of China. Markets in Hong Kong are closed, rail traffic stopped, and schools closed across the region as the rain bands approach the coast. Here is the estimated damage swath using my TAOS/TC model, based on the latest forecast from the US Joint Typhoon Warning Center (JTWC):

Click any image to expand.

On this track and intensity there are 34 Million people who will experience tropical storm winds or higher, and economic impacts will be on the order of $2 Billion US Dollars. In addition to winds, there will be some storm surge (~2 meters in places) and heavy rain that is already causing problems.

When we think of hurricanes we usually look to the US National Hurricane Center (NHC). However, the NHC is only officially responsible for storms in the Atlantic, Caribbean, Gulf, and East Pacific. For storms near Hawai’i, the Central Pacific Hurricane Center in Honolulu is responsible, from 140 degrees west to the international data line (180 W). Calvin is crossing that line today, and as of 11am ET CPHC will be taking over from NHC.

Other agencies are responsible for the rest of the world. The World Meteorological Organization, a technical agency of the UN, designates Regional Specialized Meteorological Agencies (RSMC) who are the primary forecasters for hurricanes (Typhoons, Tropical Cyclones) …

So who is the Joint Typhoon Warning Center (JTWC)? JTWC is the US Defense Department agency who provides tropical cyclone (hurricane) forecasts and warnings to US Government activities, especially DoD. They are the “primary” US source everywhere NHC/CPHC are not official (and, actually, do forecasts in those areas as well but not generally released publicly in order to avoid confusion with the official NHC forecast). Typically I use the JTWC forecasts in the rest of the world since they come through the same distribution channels and formats as NHC, and provide a globally consistent forecast. However, they are not “official” anywhere except for US Government use. I’ll do a longer post on how this works at some point, but what I do is take a weather forecast and apply that within a complex set of models (TAOS) that compute the impacts of that forecast on both the human and natural world, calculating economic impacts and populations at risk. In other words, the weather forecast (be it a human or computer model, either “in house” or, more typically, from an official agency) “drives” my models. So in my graphics you will see “TAOS/TC impact estimate based on <some forecast>”, because the forecast inputs drives the impacts as we will see in this example.

In the case of Typhoon Talim, RSMC Tokyo (the Japan Meteorological Agency) is the primary forecaster. But of course it’s not a simple as that! The China Meteorological Administration is the official government forecast agency within China, responsible for watches and warnings within the country. So how do these two forecasts compare? Let’s take a look, again using my TAOS/TC model to compute impacts from each forecast:

On the Tokyo track, impacts are a bit under $1 Billion USD (PPP) as they forecast a rapid collapse of the storm at landfall and a track shifted a bit south. By contrast, the CMA/Guangzhou (Chinese Government forecast) has impacts at over $2.7 Billion USD (PPP) as they feel the storm will maintain strength inland. Contrast with the JTWC forecast above, at $1.9 Billion. Interestingly, all three show roughly 35 Million people exposed to tropical storm force winds.

So who is “right”? Ask me that in about a year, after the storm damage has been fully tabulated and assessed! Each agency is trying to do their best, but with different tools, metrics, and concerns. In this case the differences in economic impacts for a storm less than 12 hours away from landfall are a factor of three! What I do is try to sort through what each agency is trying to do and provide an estimate tailored to the questions my clients are trying to answer. Not always a straightforward task!

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