A developing medicane takes shape over the eastern Mediterranean Sea. (NASA)

An extremely unusual “medicane” is set to lash parts of Egypt and Israel, bringing the potential for tropical storm-force winds, heavy rainfall and perhaps even coastal flooding in spots. The hybrid low pressure system, evocative of tropical cyclones yet bearing some mid-latitude characteristics, is “incredibly rare this far east in the Mediterranean,” according to the U.K. Met Office.

The well-structured system spans a 300 mile width across the extreme eastern Mediterranean Sea, parked roughly 100 miles south-southwest of Cyprus as of late afternoon Thursday Eastern Time. On satellite, it resembles a tropical cyclone, and indeed it may be somewhat close.

Medicanes feature a mix of tropical and nontropical traits, with a strictly tropical cyclone virtually unheard of in the Mediterranean.

That’s because the Mediterranean, for starters, isn’t in the tropics. The southernmost point in the Mediterranean Sea is farther north than the northernmost point in the Gulf of Mexico. Prevailing weather patterns rarely, if ever, generate tropical waves — areas of thunderstorms that are a spawning ingredient for tropical cyclones — that pass over the Mediterranean. The water temperatures are generally not warm enough to fuel a storm, either.

And, moreover, the Mediterranean is tiny compared to most cyclone-generating ocean basins.

On rare occasions, a nontropical low can meander over the Mediterranean, and a storm can form that takes on some tropical characteristics. Unlike nontropical cyclones, which are common at the mid-latitudes, medicanes feature a warm core. That requires warm sea surface temperatures.

Current waters over the eastern Mediterranean are 2 to 4 degrees warmer than normal for this time of year, and the storm is swirling over some of the warmest waters in the entire Mediterranean.


Current sea surface temperatures (in degrees Celsius) over the eastern Mediterranean. (CEAM/NCEI)

Realtime data on medicanes is somewhat tough to come by; after all, no country flies reconnaissance missions into them. Current data suggests 35 mph sustained winds are likely found at the system’s center, but weather models indicate the fledgling medicane will strengthen during the next 24 hours.

Significant impacts possible in Egypt and Israel

With a storm this unusual, the computer models meteorologists use for forecast guidance are struggling to capture how it will behave. For example, the European model backs off some on this storm’s tropical characteristics, maintaining a larger and more diffuse wind field as the system slowly drifts southeast. The American GFS model, however, intensifies the system, bringing 40-50 mph winds, a tighter circulation and even some coastal flooding concerns to extreme eastern Egypt.

Strong winds and heavy rainfall, which could cause flooding in semiarid areas, would also occur in parts of Israel, the Palestinian territories and Jordan in this scenario.

Due to the system’s diminutive size, subtle shifts in its track will have large implications both on the potential for intensification and the impacts realized on land. The most significant effects will likely arrive Saturday morning into the early afternoon local time.

A 2016 study found that medicanes are likely to become significantly stronger by the end of the century in response to climate change. Likely in response to warmer Mediterranean waters, the researchers found a likelihood for "a higher number of moderate and violent medicanes.” This is likely in response to warmer Mediterranean waters.

Since 1980, Mediterranean sea surface temperatures have increased between 1 and 2 degrees, the toastier waters are more supportive of unusual medicane-type storms.