<P> The development of medicanes often results from the vertical shift of air in the troposphere as well, resulting in a decrease in its temperature coinciding with an increase in relative humidity, creating an environment more conducive for tropical cyclone formation . This, in turn, leads to in an increase in potential energy, producing heat - induced air - sea instability . Moist air prevents the occurrence of convective downdrafts--the vertically downward movement of air--which often hinder the inception of tropical cyclones, and in such a scenario, wind shear remains minimal; overall, cold - core cut - off lows serve well for the later formation of compact surface flux - influenced warm - core lows such as medicanes . The regular genesis of cold - core upper - level lows and the infrequency of Mediterranean tropical cyclones, however, indicate that additional unusual circumstances are involved the emergence of the latter . Elevated sea surface temperatures, contrasting with cold atmospheric air, encourage atmospheric instability, especially within the troposphere . </P> <P> In general, most medicanes maintain a radius of 70 to 200 km (40 to 120 mi), last between 12 hours and 5 days, travel between 700 to 3,000 km (430 to 1,860 mi), develop an eye for less than 72 hours, and feature wind speeds of up to 144 km / h (89 mph); in addition, a majority are characterized on satellite imagery as asymmetric systems with a distinct round eye encircled by atmospheric convection . Weak rotation, similar to that in most tropical cyclones, is usually noted in a medicane's early stages, increasing with intensity; medicanes, however, often have less time to intensify, remaining weaker than most North Atlantic hurricanes and only persisting for the duration of a few days . The maximum achievable intensity of medicanes is equivalent to the lowest classification on the Saffir--Simpson hurricane wind scale, Category 1 . While the entire lifetime of a cyclone may encompass several days, most will only retain tropical characteristics for less than 24 hours . Circumstances sometimes permit the formation of smaller - scale medicanes, although the required conditions differ even from those needed by other medicanes . The development of abnormally small tropical cyclones in the Mediterranean usually requires upper - level atmospheric cyclones inducing cyclogenesis in the lower atmosphere, leading to the formation of warm - core lows, encouraged by favorable moisture, heat, and other environmental circumstances . </P> <P> Mediterranean cyclones have been compared to polar lows--cyclonic storms which typically develop in the far regions of the Northern and Southern Hemispheres--for their similarly small size and heat - related instability; however, while medicanes nearly always feature warm - core lows, polar lows are primarily cold - core . The prolonged life of medicanes and similarity to polar lows is caused primarily by origins as synoptic - scale surface lows and heat - related instability . Heavy precipitation and convection within a developing Mediterranean tropical cyclone are usually incited by the approach of an upper - level trough--an elongated area of low air pressures--bringing downstream cold air, encircling an existing low - pressure system . After this occurs, however, a considerable reduction in rainfall rates occurs despite further organization, coinciding with a decrease in previously high lightning activity as well . Although troughs will often accompany medicanes along their track, separation eventually occurs, usually in the later part of a Mediterranean tropical cyclone's life cycle . At the same time, moist air, saturated and cooled while rising into the atmosphere, then encounters the medicane and permits further development and evolution into a tropical cyclone . Many of these characteristics are also evident in polar lows . </P> <P> An unusually severe Mediterranean tropical cyclone developed on 23 September 1969 southeast of Malta, producing severe flooding . Steep pressure and temperature gradients above the Atlas mountain range were evident on 19 September, a result of cool sea air attempting to penetrate inland; south of the mountains, a lee depression--a low - pressure area in a mountainous region--developed . Under the influence of mountainous terrain, the low initially meandered northeastward . Following the entry of cool sea air, however, it recurved to the southeast before transitioning into a Saharan depression associated with a distinct cold front by 22 September . Along the front's path, desert air moved northward while cold air drifted in the opposite direction, and in northern Libya, warm arid air clashed with the cooler levant of the Mediterranean . The organization of the disturbance improved slightly further before emerging into the Mediterranean Sea on 23 September, upon which the system experienced immediate cyclogenesis, rapidly intensifying while southeast of Malta as a cold - core cut - off low, and acquiring tropical characteristics . In western Africa, meanwhile, several disturbances converged toward Mauritania and Algeria, while the medicane recurved southwestward back toward the coast, losing its closed circulation and later dissipating . </P>

Is there a hurricane season in the mediterranean