The Six Ingredients for Hurricane Formation

As we approach the 2017 Atlantic Hurricane Season [Jun 01-Nov 30], observing the sea surface temperatures [SST] indicates the “hot spots”, no pun intended, for hurricane development/intensification.  By the way, the term “hurricane” is synonymous with cyclone and typhoon, with the only difference being where they are geographically located:  Hurricanes refer to tropical cyclones located in the Atlantic and Eastern Pacific Ocean, typhoons are tropical cyclones located in the Central and Western Pacific waters. And the Indian and South Pacific Ocean basins simply refer to them by their general name, cyclones.

While SST values are one of the important determining factors to observe, cyclogenesis [the birth of a cyclone] requires a specific set of conditions to be in place in order for actual development/intensification to occur.  Let’s dissect these 6 major ingredients to fully understand the complexity of one of nature’s most powerful systems.

1.  Sea surface temperatures [SST]:  Minimum SST of 26.5 °C [79.7 °F] is necessary to provide enough heat content to “fuel” the system.  This temperature needs to be distributed through at least 50 meters [164 ft] in ocean depth.  According to Richard A. Dare and John L. McBride of the Centre for Australian Weather and Climate Research, Bureau of Meteorology in Melbourne, Australia, 98.3% of global cyclone formation occurs when SST values exceeding 25.5°C [77.9 °F].  So while meteorologists may watch thunderstorms pumping off the African Coast in anticipation of cyclone development, until there is sufficient water temperatures to fuel future development, the thunderstorm moves offshore and remains just a thunderstorm out to sea.

Atlantic Ocean basin sea surface temperatures [SST} for March 21, 2017.

2. Unstable Atmosphere/Vertical Motion: An unstable atmosphere is defined by one in which warm air continues to rise until it finds itself surrounding by air of an identical temperature. Once it finds its “home base”, this is what is known as equilibrium.  So what causes this warm air to rise?  The answer lies within the density differences between warm and cold air. Say what now?  Did things just get all science-y up in here? Well, imagine you were in a 10’ x 10’ room in the middle of a Siberian winter, with no heat; you would want to fill this room with as many people as possible to keep warm, stuffing person after person into the space to capitalize on the generated body heat.  Now imagine the same 10’ x 10’ room is located in the middle of hot Texas summer day with no A/C available; you would want to kick many of these people out of this room, ultimately to keep as much distance between yourself and any other heat generating individuals.  Now exchange people for molecules, and the idea of air density should be getting clearer; more people (molecules) in the room (air) makes the room weigh more, less people (molecules) in the same room (air) make the room weigh less.   Now you may remember that density was the amount of mass per given volume.  So, while the volume of the room stays the same, the amount of molecules (people) is what differs.  And there you have it, cold air is denser than warm air, therefore explaining why the warm air continues to rise until it achieves equilibrium.  Wow, things are getting heavy around here.

Provided there is adequate moisture present in the atmosphere, this rising warm air and moisture combine work in tandem to develop clouds.  If the rising motion continues unchecked, this will allow the clouds to continue building vertically, which now has the potential for thunderstorms.

Instability_with arrows and explanation

3.  Relative Humidity [RH]: Relative humidity is the amount of moisture available in the atmosphere, compared to how much it could fully hold [100% humidity].  High values of RH need to be present from the lower to middle portions of the atmosphere. So how much is enough?  Low values of RH cannot support cloud/thunderstorm development, and the 50% threshold of RH is borderline at best, whereas 70% and above is considered prime RH values.

4. Preexisting condition: It may begin as a simple thunderstorm, but some form of a disturbance or an area of lower pressure relative to its surroundings is the bullet to the trigger.  If a disturbance has any chance of developing into something more, it must develop or migrate into a region of the above mentioned factors.

5. Wind Shear: Wind shear is defined as the change in wind speed/direction with height.  These changes in wind direction with height must be enough to sustain a counterclockwise flow [low pressure’s spin counterclockwise in the Northern Hemisphere], but not too strong or it may move the heat and moisture away from the center of the system and essentially destroy the vertical integrity of the cloud column.

6.  Coriolis Force: This is a biggie.  This force, as a result of the earth’s rotation, induces motion to the right [Northern Hemisphere] and to the left in the Southern Hemisphere [think of launching missiles.  You don’t aim at the target, but slightly off, to compensate for the earth’s rotation.]


In addition, the amount of Coriolis force increases as the distance from the equator increases.  The sweet spot for adequate force is about 500 km [310 miles] from the equator, although formation outside of that is entirely possible.  It is physically difficult for formation to occur within 5° of the equator, because the amount of Coriolis force is simply too weak. Consequently, once a system rises above 20° latitude, the other above mentioned conditions become harder to maintain/achieve, so the ideal “Goldilocks Zone” for cyclogenesis remains between [5°- 20°].

Hurricane Movement Globally
Global tropical cyclone tracks between 1985-2005.  Photo courtesy of

So while the Atlantic Basin hurricane season is generally characterized by the Jun 01 – November 30 time frame, if the above conditions are met outside of that time frame, hurricane formation/intensification is entirely possible.  In fact, of all the Atlantic storms on record, 97% have formed within the above mentioned time frame.  So what about the other 3%?  The earliest known system has been re-analyzed to have occurred in January [1938] and the latest development has occurred in December [1954], towards the end of the month.  So while unlikely, it’s both historically and statistically conceivable.

Given the position of the earth and the amount of incoming solar radiation [insolation], ocean basins may indeed reach the required temperatures to support a breeding ground and if all other conditions are met, hurricane-a-typhoon-a-cyclone-a-comin’.



While 97% of storms form within the Jun 01-Nov 30 time frame, 6 major factors are required to produce/sustain cyclone development:

  1. SST’s > 79°F
  2. unstable atmosphere
  3. relative humidity > 60%
  4. existing disturbance
  5. adequate wind shear
  6. enough distance from the equator to experience adequate coriolis force

Stop playin’, read the whole article and learn a lil’ something!



Humidity On The Move

Observe the moisture flow in the 1000-500 mb relative humidity [RH] field.

Cool wraparound feature, as the moisture gets transported on the winds toward the departed NE low on the right hand side of the frame. Also notice the connective feature of the departed low tapping into the moisture pool from the Gulf of Mexico [GOMEX].

West coast also seeing an increase in available atmospheric moisture.

Ain’t #weather beautiful?


Dangerous Sea State Along ATL Coast

Currently, widespread sea state increases along the U.S. Atlantic Coast, with the highest conditions in vicinity of [10-15 ft].  Offshore conditions even higher, ranging within [15-30 ft].  Conditions to begin reducing from south to north, beginning Wed PM/Thu AM along the SE, Thu PM/early Fri AM along the Mid-Atlantic, and Fri AM/PM in the Northeast.#BoatersBeware


Evolution Animation of #Blizzard2017.

#Blizzard2017 will be one for the record books.  This system was a powerful combination of two different atmospheric jets, combining in just the right location, at the right position, to induce a rapidily strenghtening low pressure system just offshore.  As the system pulls northward along the coast, its position will enable strong onshore winds bringing larges amounts of moisture.

sfc analysis

Atmospherically speaking, it’s breathtakingly beautiful.

Find the 3000+ mile frontal boundary via mid level values of RH [relative humidity] and IR [infrared] satellite. Drier air moving into place behind its departure.

Current relative humidity values
Current infrared satellite, radar, and mean sea level pressure.

Cat 4 Tropical Cyclone Enawo Affecting Africa

Current IR [infrared] satellite and RH [relative humidity] view of Tropical Cyclone Enawo as it crosses Madagascar and into the Mozambique Straight.

The system made landfall as an intense Cat 4 system, with 137 mph winds. Northerly mid-level flow can be seen via the 200mb (yellow), 500 mb (green), and 850 mb (lavender) wind fields.

Drier air on the southern flank of the system will have a hard time moving northward as storm producing convection over the open water will maintain the healthy moisture field around Enawo.

The Real Deal Behind “Daylight Saving Time”

Yes, it’s “Daylight Saving Time” (DST), without the extra “s” at the end of “saving”.  So now that we’ve got this common mistake righted, back to business!

“Fall Back” and “Spring Forward”:  Remember this so-called helpful pneumonic?  It was devised to help one remember how to alter household “timekeepers” by an hour in order to keep you astronomically synchronized.  In short, it was designed to maximize “daytime” hours by capitalizing on the sun’s generosity, which is lavish in the summer and frugal in the winter.  Calendar wise, daylight saving time runs in and around April through October, while November through April is known as “standard time.  For 2017 in the Northern Hemisphere, DST will begin Sunday, March 12th, and end Sunday, November 5th.  The inverse holds true for DST in the Southern Hemisphere.

Northern hemisphere “Daylight Saving Time” schedule through the year.

With the idea borrowed from an Old English proverb, “Early to Bed, early to rise, makes a man healthy, wealthy, and wise”, Benjamin Franklin tossed around the idea in the late 18th century as a means to save on candle usage during the earlier sundown.  He figured, why not start the day an hour earlier to use the light while it was in place, thereby reducing the amount of candles burned.   It wasn’t until the late 19th century that the idea was officially proposed by New Zealander George Hudson, with the idea of giving people more sunlight in the late spring and summer, when it could be best enjoyed.  While the idea was out in the open, it was not favored.  Germany was actually the first country to adopt the process of sommerzeit (literal German for summertime) in the early 20th century.  This was done as a means to “conserve energy” by keeping people outdoors longer.  The practice of DST came and went over the earlier part of the 20th century but eventually made a necessary appearance during a global petroleum shortage in the 1970’s brought on by an OAPEC oil embargo.  Higher prices of oil per barrel forced a smart economic resolution of reducing oil dependence and relying on the natural resource of the sun’s light.  Fast forward to today, with the innovation of smarter energy practices and work hours which know no boundaries, not every country utilizes DST.

Global DST Participants_02

We know the sun doesn’t change its output, so exactly why does the change in the amount of daylight occur?  In an earlier post about spring, we discussed the Earth’s tilt as being the primary reason behind the seasons.  This tilt, in tandem with the Earth’s position around the sun, determines how much daylight each hemisphere receives.  Essentially, the amount of energy from the sun doesn’t change, but our ability to experience it, as a result of our position around the sun, is what changes.

Spring is the transitional season where the Earth changes hands from winter to summer; when the planet begins to learn towards the sun.  Along those same lines, autumn is the transitional season between summer and winter, when the Earth begins the process of tilting away from the sun.  This slow changing tilt towards (away) from the sun yields longer (shorter) amounts of time that a given hemisphere can receive sunlight.  The special day during which the Earth receives its maximum amount of sunlight is known as the “Summer Solstice”, which occurs on June 21 in the Northern Hemisphere and on December 22 in the Summer Hemisphere.

Moving the clock forward in March/April ultimately removes an hour of daylight as we approach spring and summer seasons, when we already get more sunlight. Conversely, moving the clock back an hour in November yields an additional hour of daylight, which becomes especially useful as we approach the fall and winter seasons when the amount of sunlight becomes less.  At the expense of sounding like a financial planner, consider the loss of the hour in the spring, a short term investment strategy for the upcoming fall/winter season gain; save that sunlight for a “rainy” day!

With all of this in mind, the closer one is positioned to the Northern or South Pole, the more likely they are to utilize DST. So, if you don’t like the annual “give” or “take” activity that comes with this practice, its best avoided by moving closer to the tropics, where the length of day and night varies by small enough amounts to negate the need to alter the clocks!

And lastly, just a reminder, don’t forget to move your clocks forward by an hour on Sunday, March 12th.  Ugh.



Daylight Savings Time:  marked by “Spring Forward”, begins in March/April, and means you move the clock ahead an hour, therefore losing an hour.  This is especially painful spring/summer seasons when you feel like you just got robbed!

Standard Time:  marked by “Fall Back”, begins in November, and means you move the clock back by an hour, therefore gaining an hour.  This is especially useful in the fall/winter seasons when a decrease in daylight occurs and you just want your hour back!