Severe Storms & Hurricanes Tsunami Tornadoes Snow Overload
Interestingly enough, while an HC floating at sea may theoretically be more likely to experience a hurricane several measures can be taken and/or pre-implemented, unlike existing land based city, that will make it come out of the storm with much less damage.
First of all, concerning an HC's floatstructure, realistically the only things that can severely damage a floating unit during hurricane type winds are literally "projectiles" in the form of flying debris puncturing one or more of its watertight subdivisions/compartments. However, since an HC's floating units are located "below decks", this flying debris will have to realistically originate from the sea surface itself, yet debris at sea, on its surface are virtually not present. Furthermore, wind tunnel testing can easily predetermine the required thickness that is needed for a FRP/Glass (Fiberglass Reinforced Polymer|Plastics/Fused Silica) floating unit to withstand such an impact. By simple comparison it would not be much thicker than hurricane (window) shutters, or even impact-resistance glass which are made with weaker materials - aluminum or poly carbonates, e.g., Lexan, respectively, and only require thicknesses that are less than 6.5 mm (~0.25 inches). Furthermore to do significant damage, such a flying debris would have to render an entire floating unit incapable of provide floatation and thus would have to puncture all of its compartments. Still, if one or more debris is capable of neutralizing a floating units, in an HC of minimal size or in a full HC (see here), there would be or more floating units, respectively, left standing. Therefore based on all of these parameters, the mathematical probabilities of the floatstructure of an HC completely failing during the extreme winds of a hurricane range from, at least, 1: to 1: depending on the size of the HC at the time.
Since an HC will be located, on average, hundreds of miles offshore, they will not have a shallow seafloor or rising shore that are needed to create high waves and surf surge during a hurricane. Therefore this destructive aspect of a hurricane will be a complete non-factor during a severe storm. While a great deal of wave energy may still be found in the surface of waters surrounding an HC as the storm winds will be blowing upon them, an HC surrounding m ( ft) wide HC Sea-Air Port acting as an artificial barrier Island along with its outer "barrier wall", will break in flowing waves and absorb most, if not all, of their energy. Even an extreme, "rogue waves" capable of being as high as 30 m (100 ft) in height will be broken by these structural measures and provisions.
One of the most destructive events in a hurricane occurs when widespread flooding takes place. This was particularly seen in Hurricane Katrina (2005), the costliest hurricane in U.S. history. Apart from water levees failing and causing flooding, as was the case with Hurricane Katrina, the tremendous amount of rainwater that usually falls during the hours of a hurricane can overflow sewer systems, make inland bodies of water overflow and thus cause severe flooding. Ironically enough an HC will be virtually immune from such a flooding scenario due mainly to its structural design. An HC will be built to maintain a m ( ft) clearance from the surface of waters it is floating upon. This therefore means that any rainfall can directly be discarded into the ocean, thus preventing its accumulation "on deck." In normal, situations, rainfall would be collected by HC utility systems as it is a primary, free source of freshwater. But provision will be in place where, when needed, the collection of rainwater can be bypassed (either on-demand, automatically/"failsafely", and/or, if all else would fail, manually), for its direct/straight flow to the ocean waters below.
Can an HC withstand the passing of a Tsunami wave? The answer is most likely, simply because of the coastal HC's ( of the ) being located, on average, nautical miles offshore where the average water depths are m ( ft). At theses depths, Tsunamis are no more than 1 m (3 ft) high as compared to heights up to 10.5 m (34 ft) upon arrival at shores. (The other two HC's (namely HC# 1 & HC #23) are located thousands of nautical miles from their closest shore and in areas of deep waters.)
Furthermore the HC's floating units provide advantageous m ( ft) clearance from the water.
Although a Tsunami's travel speed in deep waters is much faster than in shallower waters, this should only cause the HC to move a few centimeters/inches. Also most of the energy from the Tsunami will be absorbed by the protective HC barrier wall.
The NJK's HCs are also in very favorable positions to serve as Tsunami warning centers for their nearby coasts thus providing the much needed time for the people in these areas to evacuate the shores.
Arguably the most destructive natural force that an HC will have to protect against are those that can be exerted by a tornado (see also here, and this resourced guide). While a tornado covers a lesser area than a hurricane, their intense and concentrated rotating action has proven to be quite potent. In fact it is the many mini tornadoes that can and do form within most hurricanes that cause most of the severe wind-related damage. While, as it was explained earlier, the wind of a hurricane would not cause damage to an HC floatstructure (floating units & main deck slab), a tornado potentially can do so, unless some preventive actions are taken. First of all for a tornado to even get to an HC's floating unit, it would have to have its "spout" remain on the sea surface as it would move across part of an HC and not literally "hop" onto the HC's FRP Deck Slab where it would then not come into contact with floating units. The only place where a tornado could gain a foothold underneath the deck of an HC would be at its edges or along the sides of the planned interior canals. However the planned HC barrier wall that will be located around the outskirts of the HC and form a closed corner angle with the edges of the main deck slab will prevent this from occurring. Also, the main deck slab will be built to withstand a tornado from slicing through it, so once a tornado's spout has been forced to "hop" onto the main deck, it will not be able to slice/puncture its way back towards the sea level and thus not affect the HC's floating units.
The damages that a tornado can make to an HC would not be more than what is cause on land surfaces. Still the damages on an HC are expected to be much less than what is seen on land because HC structures and various component present on an HC will be built to withstand wind related failures, debris and destructions. Simply using FRP as the default building material, with its 'bend/give don't break' capability, instead of wood and even plexi-glass instead of glass when possible will make a significant positive difference towards the final toll.
The projected weights that an HC will be expected to support will be pre-determined as precisely as possible during its design process with an additional 5% margin, however a possible, freak extreme snow fall has to also be taken into consideration for all HC's even though this is only supposed to or possibly occur in 4 HC’s namely: HC# 10 & 11 for sure, and possibly HC #2 & 3. Still each HC is designed to be capable of supporting a snowfall of up to m ( ft) of snow. Such a one time fall of snow is not likely to happen, though it has happened as weather records. Nevertheless an HC’s planned clearance from the water surface would allow for excess snow to be quickly and easily unloaded and dumped into the waters below, particularly the snow that falls on streets and walkways (which add up to of the HC area). The clearance area under an HC also allows for snow melting systems such as hot water piping to be placed underneath streets and sidewalks, if not even green spaces, in order to immediately melt falling snow and thus prevent any accumulations. Similar systems can also be place on house and building rooftops to also prevent accumulations. July 22, 2016
National Hurricane Center Hurricane and Storms Info, Awareness, History and Preparedness.
Tsunami Tornadoes Snow Overload
Tornadoes Snow Overload