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.
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.
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.
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.
First thing first. there is still A LOT of variation that can occur 7 days out! So this briefing isn’t to serve as a forecast, but as an explanation as to the components in play.
For the last few days, we’ve been waiting to see how far S and W Irma’s trajectory would dip. Like a ball that must bounce downwards before it bounces upwards, we’ve been closely watching the expected S and W dip that Irma is undergoing this weekend. The system is expected to begin it’s more northward trajectory on Mon/Tue, and therefore a narrowing of potential outcomes will only begin then. And no that doesn’t mean the final answer will appear, but a better picture will be revealed.
Now that WSW motion is indeed in place, but it initiated slightly higher north than previously modeled. A hurricane’s position is a result of the eye location, and to put it plainly, Irma’s been acting pretty shifty-eyed. The reason for this is the multiple occurrences of EWRC [eye-wall replacement cycles]: This is when a larger eye forms around an established eye. The larger eye “chokes” off the necessary moisture and the inner eye collapses. This process does weaken or prohibits further intensification during the process, but it is usually followed by a re-strengthening once the process is complete. So if the location of the eye is slightly changing, then it stands to reason that the point of where we measure it’s S and W movement also shifts.
If you’re following the models, remember that one release does NOT indicate certainty. You’re looking for consistency from run-to-tun. The GFS (American model) comes out 4 times a day. The European model is released twice a day.
Now as mentioned prior, there are many variables that will affect the trajectory of this system: The position of a high pressure located N/NE of the system, an upper level low located to the NW of the system, high and low pressure placement over the U.S. 6-8 days from now, and Irma’s interaction with any landmasses along the way or regions of increased wind shear [how winds change with height].
Three major factors are behind Irma’s current intensity, with the first two working against:
1) Its location in a region of cooler SST’s [sea surface temperatures], but by only about 1-2 degrees cooler than what’s consider tropical fuel.
2) Drier air ahead of the system is slightly wrapping into the inner regions, which dampens cloud/thunderstorm development.
But in the ‘ole gal’s favor is that its in a region of
3) Weaker vertical wind shear of about [10-15 kts] is a hurricane’s dream, as it does not destroy the thunderstorms from building vertically but still provides enough shift to keep the circulation in place.
But….Irma is moving into a region of higher SST’s (pro), moister (pro) air, and higher shear (con).
Considering all involved, further intensification is likely.
OUTCOME: For those in the U.S, take a deep breath, and consider tightening up your hurricane plans, because come next week, the time will come to either 1) pull the trigger or 2) exhale and consider yourself to have conquered yet another week during the 2017 Atlantic Hurricane Season.
But if you’re asking, “What would YOU do”, well, on this end, supplies are in place; because why not. Because what better way to actually relax this labor day weekend than to know whatever happens next week, as the picture sharpens, things are in place now. [Think of people who waited until the last minute to find solar eclipse glasses; how well did that work out?]
So, stay tuned, stay aware, and DO NOT buy into the hype anytime over the next 2 days.
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.
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.
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.
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 MSMünchen, 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 MSMünchen 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.
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.
A squall Line as seen on radar, ahead of the main boundary line.
Squall Line as seen from Lauderdale-By-The-Sea | Photo by Weather Forecast Solutions
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.
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.
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.
For all the #boaters in the [aquatic] house, increased conditions in vicinity of [20-25 kts] winds and [4-6 ft] seas behind the frontal boundary [white line] in the NW Gulf of Mexico.
These increases will continue to propagate eastward through the Gulf through early Tuesday, arriving along the East Gulf waters by Monday afternoon. Strong northerly winds will continue to build in behind the boundary, likely remaining in and around [10-15 kts] through early Monday morning.
Elsewhere, southerly flow along the U.S. East coast will continue to increase through midweek, with sea heights additionally increasing beyond [6 ft] as the weak low off the East Coast of #Florida lifts northwards and towards the #MidAtlantic.
NOTE: Img indicates significant wave heights in ft and winds in kts.
Same Atlantic flow plus Gulf of Mexico moisture piggybacking on the southeastern and southerly winds into the interior Gulf Coast and Southeast U.S. states, pooling in the vicinity of the slowly northward drifting frontal boundary.
Daytime heating will further induce instability in the region, igniting showers and #thunderstorms today and tonight. Some showers and storms will produce locally heavy rains, with flooding may be a concern in some areas.
Cyclone Cook is currently aiming towards New Zealand, with 30-40 kt winds along the East Coast of the North Island and off the East Coast of the South Island. Winds will become more northerly as the system continues to slide southward through the remainder Friday and into early Saturday [local NZ time]. Winds in excess of 20kts will remain along the North Island through Saturday afternoon [local NZ time], subsiding below 15 kts by Sunday evening/early Monday [local NZ time]
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.
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.
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°].
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  and the latest development has occurred in December , 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:
SST’s > 79°F
relative humidity > 60%
adequate wind shear
enough distance from the equator to experience adequate coriolis force
Stop playin’, read the whole article and learn a lil’ something!