Tropical Cyclone Movement Speed
The theme for today’s #30DayMapChallenge is MOVEMENT. So in this map I plot the movement speed of Tropical Cyclones (TCs) in a small chunk of the Western Pacific Ocean.
Now, this map is intentionally confusing as there are too many lines. I did this to show that plotting too many data points (or lines in this case) is not always visually appealing. Unless that is the message you want to get across (there are too many Tropical Cyclones!) just like in a previous map I did (see Tropical Cyclone Density and Tracks).
Now, in a previous discussion from the density map, I initially hypothesized that Tropical Cyclones speed up as they traverse land as the TC points are most dense (brighter in the map) over the West of the Philippine Sea, and, errr, the West Philippine Sea.
A paper by Wu and Choy (2015) supports this argument by concluding that TCs that make landfall in Luzon are likely to accelerate as they approach Luzon, and then decelerate as they leave. However, looking further at their analysis the increase in movement speed before landfall is only around 2 knots (3.70kph), with the decrease after landfall at ~3 knots (5.56kph). With movement speeds over the Philippines around 5 knots to 20 knots, the 2 knot difference might arguably be not that significant (please correct me if I’m wrong).
However, looking at it in a different perspective, I tried comparing the median movement speed a day before landfall and a day after landfall, and found no significant difference. I have yet to look at overland speed. But looking at all the data I currently have, it is safe to say that most TCs that make landfall and track straight spend less than a day over the Philippines (unless you are Typhoon Parma and Fujiwhara takes over your soul).
What’s different is that TCs that don’t make landfall and curve over the ocean are usually slower. Although I still have to check the numbers, removing all other faster line segments (>5 knots) yield very squiggly lines. Similarly, these mostly traverse over the ocean with few segments over land. It looks like these curly tracks caused the brighter spots in the previous density map. I need to do more research but I have a feeling that these curly TCs are the ones that cause more rain.
Data used in this map came from the International Best Track Archive for Climate Stewardship (IBTrACS) and processed using QGIS. IBTrACS is a very rich dataset that has more than 100 years of TC data. If you want to start playing with the data but have a hard time starting (as the dataset is very very intimidating), do send me a message! I’ll see how I can help.
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Data source:
https://www.ncdc.noaa.gov/ibtracs/
References:
Man-chi, Wu, & Chun-Wing, Choy (2015). An Observational Study of the Changes in the Intensity and Motion of Tropical Cyclones Crossing Luzon. Tropical Cyclone Research and Review, 4(3), 15. https://doi.org/10.6057/2015TCRRh3.01
