Subject: G1) When is hurricane season? Contributed by Neal Dorst (HRD) The Atlantic hurricane season is officially from 1 June to 30
November. There is nothing magical in these dates, and hurricanes
have occurred outside of these six months, but these dates were
selected to encompass over 97% of tropical activity. When the
Weather Bureau organized its new hurricane warning network in
1935 it scheduled a special telegraph line to connect the various
centers to run from June 15th through November 15th. Those
remained the start and end dates of the \’official\’ season until
1965, when it was decided to start at the begining of the month
of June and run until the end of November. The Atlantic basin shows a very peaked season from August through October,
with 78% of the tropical storm days, 87% of the minor (Saffir-Simpson
Scale categories 1 and 2 –
) hurricane days, and 96% of the major (Saffir-Simpson categories 3, 4 and 5) hurricane days occurring then ( ). Maximum activity is in early to mid September. Once in a few years there may be a tropical cyclone occurring \”out of season\” – primarily in May or December. (For more detailed information, see – \”What is my chance of having a tropical storm or hurricane strike by each month? \”) The Northeast Pacific basin has a broader peak with activity beginning in late May or early June and going until late October or early November with a peak in storminess in late August/early September.
NHC\’s official dates for this basin are from May 15th to November 30th. The Northwest Pacific basin has tropical cyclones occurring all year round regularly. There is no official definition of typhoon season for this reason. There is a distinct minimum in February and the first half of March, and the main season goes from July to November with a peak in late August/early September. The North Indian basin has a double peak of activity in May and November though tropical cyclones are seen from April to December. The severe cyclonic storms (>33 m/s winds [76 mph]) occur almost exclusively from April to June and late September to early December. The Southwest Indian and Australian/Southeast Indian basins have very similar annual cycles with tropical cyclones beginning in late October/early November, reaching a double peak in activity – one in mid-January and one in mid-February to early March, and then ending in May. The Australian/Southeast Indian basin February lull in activity is a bit more pronounced than the Southwest Indian basin\’s lull.
The Australian/Southwest Pacific basin begin with tropical cyclone activity in late October/early November, reaches a single peak in late February/early March, and then fades out in early May. Globally, September is the most active month and May is the least active month. Last Revised : June 2, 2016 From mid-August through mid-October, the activity spikes, accounting for 78 percent of the tropical storm days, 87 percent of the category 1 and 2 hurricane days ( ), and a whopping 96 percent of the major (category 3, 4 and 5) hurricane days. Why does this peak period of activity begin so deep into summer? There certainly is no lack of disturbances throughout the entire six-month hurricane season. Tropical waves are coming off of the coast of Africa roughly every three days, and the very early and late parts of the year provide additional types of potential seedlings. What s different, though, is the environment that these potential tropical cyclones tend to encounter. Both dynamics (wind factors) and thermodynamics (temperature and moisture) play a role. Wind shear, which can tear disturbances apart before they strengthen, is strong in May, but gradually fades through June and July, reaching a minimum by mid to late August.
This minimum in the shear combines with favorable thermodynamics ocean temperatures in the deep tropics that increase with each day of summer sun, warmer air temperatures, and increasing atmospheric moisture. When the dynamics and thermodynamics are in sync, as they often are from mid-August through early October, disturbances like African tropical waves can easily strengthen. The statistical peak day of the hurricane season the day you are most likely to find a tropical cyclone somewhere in the Atlantic basin is September 10th. By mid-October, when winter begins to give autumn a little nudge, strong upper-level winds bring increased wind shear to much of the Atlantic basin, while both the air and water temperatures cool. The season is not over yet, but the areas where storms can form become limited. One thing that doesn t change as we move into and out of the peak of season is the need to be vigilant and. Because it doesn t matter whether activity levels are high or low it only takes one storm to make it a bad year for you. For more information about hurricane season please visit NOAA\’s.