Surfline user Josh writes:
“Dearest Rad Forecasters,
Why does the South Pacific act up (send swell) during its winter & why does the North Pacific send us swell during winter? Essentially I see a tension between the fact that the hemisphere which is going through winter produces the strongest swell producing storms and the fact that hurricanes are strengthened by warmer waters (I’m assuming from thermal energy from the sun) which are associated with summer/fall. While in each hemisphere’s respective summer the swell machine is dormant. Am I comparing apples to oranges?
Thanks,
Josh”
Hi Josh,
Excellent question and one that comes up from time to time. I have also had several friends ask this same exact question.
And there is a simple response for this – differential heating over the earth’s surface. Ok – that sounds all fancy and stuff but what does it mean in laymen’s terms? Well, the earth is unevenly heated; we generally have warm air in the tropics and cold air over the polar regions. This creates a contrast in temperatures over the globe between the equator and the poles. Weather, in the form of low and high pressure systems, acts to rearrange these temperatures in an ongoing effort to balance out this temperature difference between the hot and cold regions on the earth, a re-distribution of heat!
So now the next question invariably pops up – what purpose do tropical cyclones have in this whole scheme? Well the overall essence of the work that tropical systems perform in trying to re-distribute heat is the same. Only the processes by which this is done are different. Just as the air becomes generally colder from the equator to the poles, the oceans also generally become cooler from the equator to the poles. Now we do have ocean currents driven by the winds that act to redistribute this heat (i.e. Florida Current and the Gulf Stream) but the waters that make up the ocean can hold vast quantities of heat, much more so than air per unit quantity. Tropical cyclones extract this heat from the oceans, this in turn drives the tropical cyclone and these tropical cyclones redistribute this heat as they track across the globe. This distribution is generally from the equator to the poles as most tropical cyclones invariably will track generally northward.
So as you can see, weather has a never ending purpose in trying to balance out the temperature difference across the earth. As we approach the winter season the temperature contrast between the equator and the poles will increase and we expect the weather to act accordingly in its never ending quest to redistribute heat – and hopefully bring us some surf in the process!’
In conclusion, during the each respective hemisphere’s winter, we have the largest contrast in temperatures between the poles and the equator. In turn this large temperature contrast cranks out the strongest storms. Conversely, in the summer, the pole to equator temperature gradient is comparatively weaker and thus we see less storm activity in the summer hemisphere.
Hope this helps and feel free to fire back with any further questions.
Best,
Mike Watson
Surfline East Coast Manager/Forecaster
