Treacherous, frozen latitudes becoming hot destinations

Once upon a time, the ideal yachting expedition would involve calm seas, warm breezes and smooth sailing. The yachting season would follow the global circuit of chasing the sun and festivals, with promises of balmy nights and sun-soaked days. Now, however, extreme destinations are becoming a popular alternative for those who want their morning coffee served with a side of adrenaline. While the treacherous conditions may require the heartiest of captains and crew, the rewards of exciting adventure and exquisite landscapes are drawing many to the rugged ends of the Earth.

Some of the most obvious and immediate dangers of yachting through such high-latitude regions are the screaming winds and high seas associated with passing low pressure systems, but this does not discount other difficulties such as frigid temperatures, little or no available assistance in the event of emergency, drifting ice and thick, blinding fog.

When it comes to the volatile weather in the North polar regions, storm systems piggy back on the eastern-racing jet stream. When these systems reach the Eastern Seaboard and move offshore into the open Atlantic, they are often energized by the warm tropical waters hitchhiking along the Gulf Stream. These systems can often produce conditions in excess of 40-knot winds and 20-foot seas, with one storm after the next for months on end. The summer months are the best bet for lengthier breaks between storm systems, but no season is immune to nature’s fury. Taking into consideration a yacht’s top speed, maneuvering around the rapidly deteriorating sea state may prove to be challenging, and obtaining weather intelligence prior to departing is well-advised.

The infamous Northwest Passage, which connects the Atlantic Ocean to the Pacific Ocean via the Arctic waters around Greenland and through Canada, offers an alternative route that shaves off a considerable amount of time from the normal route.  With diminishing ice volume in the region, the waters have become more navigable, and were most recently crossed in 2016 by the cruise ship Crystal Serenity, which took 28 days.

Looking toward extreme destinations in the Southern Hemisphere, the subantarctic islands to the south of New Zealand and South America can be the destination or merely a stop along the way to the actual Antarctic continent itself. The conditions in this region of the world tend to remain hostile year-round. Minimal land mass in the Southern Hemisphere allows for storm systems to travel thousands of miles uninterrupted. With little to no frictional effects of land to slow these winds, storms are able to maintain their edge, giving way to the nicknames associated with their line of latitude, such as the “Roaring Forties,” “Furious Fifties,” and “Screaming Sixties.” Long-range swells associated with these winds make the higher latitude Southern Hemisphere seas very tumultuous.

Whether it’s the promise of isolation that draws the visitor, as the more common yachting circuit may yield congested harbors and ports, or the promise of nightly auroras and glowing, moonlit glaciers, extreme destinations are on the rise. Seafarer, beware – it is not for the faint of heart.

Advertisements

Roll Clouds: The Most Unusual Cloud in the Skies

Turning towards the sky, one can’t help but become mesmerized by beauty and movement of the different clouds that flow across the atmosphere.  One of the most peculiar looking clouds, arcus clouds, are horizontal elongated tube-like clouds that can occur all over the world.  A subgenre of arcus clouds known as roll clouds, are even more atypical as they are detached from any other cloud features.

Roll-cloud
Roll cloud seen on January 25th 2009, on “Las Olas Beach”, located in “Punta del Este”, Uruguay, by Daniela Mirner Eberl.

While roll clouds can occur in many places, such as Germany, Canada, South Africa, Brazil, Uruguay, and even Florida, they are regionally known as “Morning Glory” clouds along the North Australian Coast, more specifically over the Cape York Peninsula and Gulf of Carpentaria.  The clouds are so named as a result of their early morning appearance, and frequently occur during late September and through early October in this region.  These phenomenal clouds may be on the order of 400-600 miles in length, ½ – 1 mile high, and may move as fast as 40 miles per hour.

As with any cloud, moisture must be present in order for water vapor to condense into water droplets.  Morning Glories tend to occur when humidity values are elevated and a clash of different air masses.  Once moisture levels are adequate, these clouds may form as a result of drastic temperature changes in air masses ahead of a thunderstorm, frontal boundary, or sea breeze.

MorningGloryCloudBurketownFromPlane
Morning glory cloud formation taken from a plane near Burketown (plane heading to Normanton) in QLD, Australia, 11 August 2009, by Mick Petroff

To understand the physical nature of a cloud, let’s first take a look at the relationship between air density and temperature.  Cold air is heavier than warm air as a result of more molecules per volume.

density

To better understand this, imagine a 10’ x 10’ unheated room in the middle of a Siberian winter.  For a person to keep warm, they would want to fill this room with as many other people as possible, capitalizing on generated body heat.  Now imagine that same 10’ x 10’ room located in the middle of hot Texas summer day with no available air conditioning.  In this scenario, a person may want to remove a majority of the heat generating bodies.  So if we exchange molecules for people in the above example, cold air has more molecules than warm air in the same amount of space, therefore making cold air denser (heavier) than warm air. This is what makes cold air sink downwards and warmer air upwards by nature.

A sudden influx of cold air can also force warm surface air to rapidly rise, which is often the case of what happens when cold air rushes out ahead of a thunderstorm or when sea breezes occur from differential daytime heating.  A gust front is the downward and outward rush of the colder/heavier air from within a thunderstorm, usually followed by strong winds, heavy rain, and possible hail within minutes.  An extremely strong gust front rush out faster, detaching from the parent storm, and creating a roll cloud.  Sea breeze circulations occur as the sun heats land and sea surfaces differently, creating an onshore flow during the day and offshore flow during the night hours.  When an extremely strong sea breeze occurs in the evening, the elevated chances of a Morning Glory cloud occurs the following morning.

While there’s no shortage of atmospheric phenomena to excite the average observer, it is without doubt that encountering a roll cloud is an incredible sight and definitely on any weather lover’s bucket list.

_____

This article was published in our monthly column within The Triton  newspaper (Nautical News for Captain and Crews), and can additionally be found here.

Sea Science: Weather Lore Jibes With Modern Science

Before the invention and integration of high-tech weather instruments such as satellites, radar, and computer models, individuals often used environmental observations to determine impending weather. At a recent lunch with retired Captain Terry Pope, the topic of historical seafaring methods of weather prediction came up. For example, captains sometimes kept an elderly sailor on board whose rheumatic pains could warn of incoming low pressure or rain.

Many weather proverbs were born of natural observations, with sailors and farmers adding credibility to their catchiness. It turns out that examining these sayings through a scientific lens actually proves that one really can trust the great salty grandfathers of the high seas.

One of the most well-known of these sayings is “Red sky at night, sailor’s delight; red sky at morning, sailors take warning.” In order to make sense of this proverb, there are a couple of scientific points to understand: the vertical direction of air during high/low pressures, the general movement of weather patterns from west to east, and how the human eye perceives the specific colors of visible light.

Of all the colors of the visible light spectrum, red has the longest wavelength and violet has the shortest. Therefore, when traveling long distances or through a region of atmospheric contaminants, such as dust or pollution, the shorter wavelength colors are scattered while the longer wavelength colors make it through. This is often why we see red and orange at sunset, when the sun is lowest on the horizon and the light has to travel the farthest.  This also explains why the sun appears white during noontime hours; the sun’s position directly overhead means the light has the shortest distance to travel, with all colors effectively making the journey to the human eye. Another way to understand this concept is by observing something in the dark. The object doesn’t change color, but the human eye is unable to perceive it because of the absence of light, so it appears black.

Sunset_Web Version_With Logo
The warm colors of sunset are a resultant of the longer wavelengths associated with reds, oranges, and yellows.

With the sun setting to the west, red color indicates sinking/drier air associated with an incoming high pressure, which prohibits the rising air and upward cloud development that lead to thunderstorms. Conversely, a red sunrise to the east indicates the high pressure is to the east of an observer’s position, meaning a relatively low pressure is located to the west.  The rising air associated with a low pressure instigates clouds that, with enough vertical ascent, lead to the potential for stormy weather.

Another useful proverb, “Mackerel skies and mares’ tails make tall ships carry low sails,” scientifically makes the grade as well.

The names of clouds are often a Latin derivation that describe the clouds’ pattern, the type of particles they contain or their height in the atmosphere. Clouds are a useful way for an observer to determine the state of the atmosphere at a given time. In Latin, cirrus means “curl” and cumulus means “mass or pile.” So when cirrocumulus clouds are observed in tandem with cirrus clouds, it generally indicates convection occurring at high altitudes, and usually precedes rain within a day.

Cirrocumulus_Mackeral Sky_Web Version_With Logo
Cirrocumulus clouds are often referred to “mackerel sky” for their resemblance to the fish’s scales.

Cirrocumulus clouds also appear quite similar to the scales of a mackerel fish, and cirrus clouds are much like the strands of a mare’s tail, so this saying delivers a general warning to lower the sails, as the higher winds associated with thunderstorms are impending.

“A wind from the south, has rain in its mouth” is a third axiom that jibes with sound science. Winds will always move from high to low pressure, so a breeze from the south will indicate a high pressure is situated to the south or southeast of a location, blowing towards a lower pressure located somewhere to the north or northwest.

High to Low_Web Version_With Logo
Winds will move from high to low pressure.

Since low pressure induces rising air, cloud formation becomes possible.  With enough moisture and rising air, storm development occurs, increasing the possibility of precipitation. Another useful fact to consider is that the faster clouds move, the more imminent the ​arrival of a frontal boundary associated with an advancing low pressure.

Accurate and long-range weather forecasts depend on technology. Without its aid, the time frame for a credible forecast drastically drops from five days to about 24-48 hours. Even so, it’s good to know that if modern weather forecasting tools are unavailable or not working for some reason, a pretty credible weather forecast can still be produced by simply turning to the sky.

This article was published in our monthly column within The Triton newspaper (Nautical News for Captain and Crews), and can additionally be found here.

Leonid Meteor Shower This Weekend

Meteor shower alert this weekend!
 
WHEN: This weekend marks the occurrence of the #Leonid #meteor shower, which tends to be one of the best and brightest every year. The peak of this shower (Friday night into early Saturday morning) also aligns with a new moon, meaning much darker conditions for seeing up to 10-25 meteors per hour! Of course, this is a weather permitting scenario.
 
WHERE: Face the east, look up, locate the big dipper (the big pot), and follow a “3 fist distance” line towards the constellation Leo (as seen in the image)
Wolf-359-UMa-Leo-chart
 
WHO: As of now, viewing conditions look to be clear/partly clear for a majority of the United States. The Southeast, Northeast, Southwest, Central and Southern Rockies, and portions of the West Coast and Mid-Atlantic will be in luck. Cloud coverage will likely obstruct views in the Central and Northern Plains, the Great Lakes, and the Middle-to-Upper Mississippi Valley. However check your local weather service forecast by entering your zip code here: http://www.weather.gov/
 
HOW: Exactly what and how does this happen? As our planet orbits the sun, so do comets. This shower is a result of the Earth crossing paths with the debris trail associated with the Temple-Tuttle comet. Much of this debris enters into our atmosphere, but burns up due to frictional effects, hence the meteors that we see!
 
Sometimes the comets’ approach is closer than other years, turning a meteor shower into a meteor storm. While this year isn’t going to be a closest approach scenario, clear skies and the new moon will aid in producing a memorable event for many.
 
This show would definitely be worth the drive into a dark(er) location to observe this phenomena. Get out there, send us your pics, and inspire others to appreciate this beautiful event!
 
#AdventureIsOutThere

Weathering Through the Yachting Season

Weather conditions are generally what drive the popularity of yachting season around the world. Most voyages are seeking the moderately warm breezes, long days, and pleasant waters.  Suffice to say, no one is pursuing 15 ft waves, freezing temperatures, or torrential rains.  While other determining factors such as cultural events, boat shows, and festivals also factor into intended routes, the weather is the general dictator on the scene.

Global pressure patterns will determine where and how wind patterns work, which ultimately control the associated wave heights and relative positioning of ocean currents.  Much like the phrase “work smarter not harder”, yachting also follows the same train of thought:  work with the elements and not against!  Riding with the currents can often save on fuel and can ensure a speedier ride.  It’s no coincidence that many of the global routes follow the natural flow of the water.

ESS_PasteBitmap02948
Transoceanic voyages often follow the major ocean currents

Another major factor is precipitation patterns, as regional monsoon seasons can make for an extended wet ride. A seasonal wind pattern shift, such as ENSO (El Niño Southern Oscillation), is defined as a longitudinal shift in pressure patterns and winds which occur on average, every 2-7 years.

ELNINOJPEG
El Niño typically weaken or reverse the easterly trade winds to become westerly, as seen in this image.  This enhances warmer water to reach the Eastern Pacific, which further increases rain potential.

In the warm phase of ENSO, El Niño, easterly winds weaken or reverse.  This causes the warmer waters to shift from the Western/Central Pacific towards the Eastern Pacific, piling up along the South America coast. The warmer waters instigate thunderstorm development, so in turn, higher precipitation occurs.  Another side effect of the excess water is that it reduces upwelling, which is the ability of the deeper, colder, more nutrient-rich water to make its way to the surface. Ocean currents are related to water temperatures, so this shift alters the local currents.

LA NINAJPEG
La Niña enhances the easterly trade winds, forcing water mass to pile into the Western Pacific. As a result, this elevates precipitation in the Western Pacific.   Meanwhile deeper (cooler) water upwells in the Eastern Pacific, which can limit thunderstorm activity.

Conversely, during the cool phase of ENSO, La Niña, the exact opposite occurs:  The easterly winds strengthen, which piles the warmer waters towards the West Pacific.  This migration of water from the East to the West makes it easier for upwelling to occur along South America.  The repositioned warmer waters over the West Pacific increase thunderstorm activity, and therefore precipitation potential.

Further examination of popular global destinations reveal that prime yachting season aligns with capitalizing on the best weather that each location has to offer:

Yearly Chart_300dpi
Peak months for yachting around the world, often follow the seasons.

The tail ends months of peak seasons tend to be the most financially affordable, as they occur while seasons are still transitioning from undesirable winds/rain/temperatures to the more preferred conditions.  While the weather can still somewhat be iffy, this is generally when dock space, berths, and anchorages are plentiful and tourists are minimal.  As yacht owners and charters seek sublime weather, peak seasonal time also brings overwhelming tourists and limited availability, hence higher prices.

PAC Headings
Global boating tracks, created via OceanPassages

Of course some locations are blessed with a year round type yachting season, such as Florida or the Caribbean, maritime SE Asia, or generally anywhere that is located near the equator.  Approximately 12 hours of daylight bless the equatorial regions, with daylight decreasing as you head north of south of this line.  While that ideally works for most of the year, the real caveat occurs when this excessive heat produces or strengthens tropical cyclones.  Rapid intensification or a change in track may force a yacht to redirect its route with minimal notice, or scurry towards an available hurricane hole.

Predicting and tracking the development and movement of tropical cyclones can be very tricky, as it involves a working knowledge of a four dimensional science: How things are changing 1) from east to west 2) from north to south 3) from the surface of the earth throughout the atmospheric column 4) with time. Recent activity surrounding Hurricane Harvey was a prime example of how a tropical system can intensify in a very short amount of time, as it went from a category 1 [74-95 mph] to minimum category 4 [130-156mph] in less than 24 hours.

The open ocean is a nautical playground for many, to which weather writes the rules.  Knowing the best time to take to the high seas is important, to make the best of your adventure and your time!

Severe Weather on the High Seas

Nothing makes a body feel as protected from the elements as a solid set of four walls and an up-to-code reinforced roof, but these protective features may not be present when active weather strikes.  Many seafarers find themselves subjected to harsh elements, putting them at the mercy of the skies above and the waves alongside their trusted vessels.

When it comes to the ocean, nothing “stirs the pot” like the wind; and the winds are a response to pressure differences.  More specifically, winds move from high to low values of pressure, and the greater the differences between the pressure fields, the faster the wind moves.  A good way to visualize this process is to imagine a ball rolling down a hill: the steeper the slope of the hill, the faster the ball will roll. Oh gravity, thou are a heartless force.

Ball Trajectory
The steeper slope will yield a faster speed as a result of gravity.

High pressures can ultimately be thought of as “hills”, the low pressures as the “dips”, and the ball is the “wind”.  So when analyzing atmospheric pressure patterns, much like a contour elevation map would indicate the steepness or grade to a hiker, tightly spaced pressure contours indicate a steep pressure change pattern, hence higher winds.

3D render of Pressure
Winds will flow from high to low pressures, and the steeper the slope, the faster the winds.
Pressure Gradients and Winds_02
Tightened pressure contours between a high and low pressure indicates a steep slope, which yields faster moving winds.

So the wind blows and the waves react as a result. Now depending on the size and location of the pressure patterns, winds and therefore waves of various sizes can be produced and travel away from their origin location.  Wind waves are a result of local winds blowing across the surface of the water that eventually break or reach a shoreline.

Waves

If no deterrent is present, these waves have the ability to propagate over hundreds of miles as a result of their momentum.  This is known as groundswell

Waves can often aid a vessel along its course, acting like a turbocharged engine to work in tandem with the boats own gas/diesel power.  However there are the other instances in which the waves become the foe.  Increased wave heights, including the elusive rogue waves can roll and/or even break a vessel, overpower engines or snap rudders, leaving a craft at the mercy of the winds.

While most know the tale of the RMS Titanic, other maritime disasters have encountered similar fates as a potential result of winds and their respective waves. A 656 ft German merchant ship, the MS München, departed Bremerhaven, Germany on December 7th, 1978 on a transatlantic voyage towards Savannah, GA.  In the early morning hours of December 12, the MS München sent out an S.O.S. signal, with its last reported position.  All search efforts were officially called off on December 22, with emergency buoys, life rafts, life vests and belts, and lifeboats retrieved from search operations and random encounters. The MS München was never located, but via investigations done on the salvaged lifeboats, it has been theorized that via severe weather, she likely succumbed to a series of large waves which both broke over the bow and eventually flooded the vessel, causing it to sink.

While it may be easier to associate poor conditions with big patterns, sometimes small scale phenomena can produced localized increases not seen in the big picture.  Two examples of this would be squall lines and water spouts.

Waterspouts can be sub-categorized into tornadic and non-tornadic, as a result of their formation source. The fair-weather types are most frequent, and are considered non-tornadic in nature, meaning they aren’t associated with a supercell thunderstorm as are the rarer tornadic waterspouts. Typical non-tornadic waterspouts start forming on ocean/lake surface and rise up to meet the base of a parent cloud.  They tend to last less than 20 minutes and produce winds less than 70mph, which would classify it as the equivalent of an EF-0 tornado.  Tornadic water spouts are a result of a rotating cloud which produces a tornado that then descends and connects to the surface of a body of water.  While limited in space and time, either type of waterspouts can locally whip up winds and waters, and boaters are advised to stay clear.

Waterspouts_03
Waterspouts in St. Thomas, US Virgin Islands | Photo by Erickson
Waterspouts_02
Waterspouts on the Mediterranean | Photo by Mehmet Gökyigit
Waterspouts
Waterspouts off the coast of Turkey | Photo by Tufancetiner

Tornadic waterspouts can also be associated with squall lines, which is a typically narrow but elongated band of intense thunderstorms.  The formation of a squall line in the near or offshore waters is usually ahead with an oncoming cold front associated with a low pressure.  While generally measuring about 10-20 miles wide, squall lines can stretch for hundreds of miles, and are capable of producing, tornadoes/waterspouts, damaging winds, and frequent lightning.  An incoming frontal boundary from the West or Northwest will alter winds in a location as follows:  Initial winds will be from the east/southeast to south, as the winds begin blowing from the local higher pressure towards the incoming lower pressure.  As the frontal boundary nears, winds will become south/southwest, finally becoming west/northwest as it departs. When a squall line approaches ahead of the frontal boundary, wind shifts can be sudden and fierce which leaves little time for vessel preparation.

From the small scale back to the large, no other weather phenomena has the power and expansive reach than that of a tropical cyclone.  The amount of energy generated during the evaporation and condensation processes that produce the clouds/rain is almost 200 times the world’s electrical generating abilities, while the amount generated via the wind is roughly half of the world’s electrical generating abilities.  The movement across the ocean basins can generate long range swells that can be felt several hundred miles away.  Navigating a vessel around the associated increases can be tricky and requires advanced knowledge of environmental factors to determine potential storm trajectories.

Tropical_Vis and RH
Visible satellite, mid-level relative humidity, and steering flow of 2016’s Hurricane Matthew.  This image was produced while Matthew was a category 3 system; less than 8 hrs later, Matthew would briefly strengthen into a category 5 system.  This system made 4 separate landfalls:  Haiti [cat 4], Cuba [cat 4], The Bahamas [cat 3 & 4], and South Carolina [cat 1]

When interaction with a system is imminent, understanding how to circumnavigating via the “Front Right Quadrant” [FRQ] becomes key.  If one was to intersect the system with a “+” sign, the FRQ is defined as the front and right side of the system, relative to the storms forward motion. This is where the storm’s winds work in tandem with the directional wind to produce the highest winds of the cyclone.  In other words, the side to be avoided if at all possible.

FRQ
The front right quadrant, relative to the direction of motion, indicates where the strongest winds of a tropical cyclone are located.  This is where the systems’ winds work in tandem with the motion.

While there are many hazards out to sea, advanced planning and a working knowledge of the science behind these risks can help minimize disasters out to sea.  Knowledge is power and coupled with a bit of luck, here’s hoping for fair winds and following seas.

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.

SST
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.]

coriolis_forceCoriolis

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 Nasa.gov

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’.

____________

TL;DR

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!

____________