The Maltese Islands have received a measly 20.4 mm out of the 203.8 mm we normally expect during the months of December and January. Climate values suggest that these two months should make up the wettest part of the year. Any rain in the coming weeks will continue to be isolated and infrequent. But what is behind this? It is a positive North Atlantic Oscillation (NAO). The NAO is the interaction between a general low pressure near Iceland (the Icelandic Low) and a general high pressure near the Azores Islands (Azores High). Over time, we notice fluctuations in their respective strengths. In its positive state, the Azores High is stronger than normal whilst the Icelandic Low is deeper. This alters the path of the jet stream. The jet stream is a very strong air current that flows west to east across the northern hemisphere, altering temperature and precipitation as portions of it dip southward or crest northward. In a positive NAO, the jet stream keeps to the north. This allows warm air from over Africa ro rise far more freely towards the Mediterranean and Europe. It also prevents low pressure systems forming over the Atlantic from reaching the Mediterranean and southern Europe, as they are deviated to the north. As a result the Maltese Islands experience a warmer and drier winter. A variable NAO is part of a cycle. We have had similar winters on numerous occasions in the past. The most notable include 1990, 1996, 1998, 2000, 2009 and 2015. The latter was record-breaking. Scientists have discovered a very serious abnormality, however. The oscillations are becoming increasingly unpredictable. They have been varying more dramatically recently. Scientists say the loss of Arctic sea ice due to global warming is causing the Icelandic Low to weaken. This would mean a more frequent positive NAO, and hence an increase in the frequency of warm and dry winters for the Maltese Islands. Summers will also become longer and hotter because of this. Of course, winter has some more weeks to go, so the state of the NAO’s could shift. As winter progresses, the chance of a shift becomes less likely, however.

Il-Gżejjer Maltin sa issa ħadu biss 20.4 mm minn 203.8 mm li ssoltu jieħdu matul ix-xhur ta’ Diċembru u Jannar. Valuri klimatiċi jindikaw li x-xhur ta’ Diċembru u Jannar normalment ikunu l-aktar parti mxarrba tas-sena. Minkejja dan, ix-xita matul il-ġimgħa li ġejjin mistennija li tibqa tkun iżolata u infrekwenti. Imma x’inhu l-kaġun ta’ dan? Tissejjaħ North Atlantic Oscillation pożittiva. NAO tirrapreżenta l-interazzjoni bejn pressjoni baxxa ħdejn l-Iżlanda (Icelandic Low) u pressjoni għolja ħdejn il-Gżejjer Ażore (Azores High). Ninnutaw li l-qawwa ta’ dawn tvarja minn żmien għal ieħor. Fi stat pożittiv, l-Azores High tkun aktar qawwija minn normal, filwaqt li l-Icelandic Low tkun aktar intensa. Dan iwassal biex il-jet stream ibiddel il-pożizzjoni tiegħu. Il-jet stream huwa kurrent ta’ arja qawwi ħafna miexi mill-punent lejn il-lvant fl-emisfera ta’ fuq, u jinfluwenza t-temperatura u x-xita hekk kif dan iserrep. Meta l-NAO tkun f’arranġament pożittiv, il-jet stream iżżomm il-fuq. Dan jippermetti li arja sħuna minn fuq l-Afrika testendi lejn il-Mediterran u l-Ewropa aktar minn normal. Din tipprevjeni wkoll sistemi ta’ pressjoni baxxa li jiżviluppaw fuq l-Atlantiku minn li jilħqu l-Mediterran u n-nofsinhar ta’ l-Ewropa, hekk kif dawn ikunu mbuttati lejn it-tramuntana. Ir-riżultat ta’ dan hija xitwa aktar sħuna u niexfa fuq il-Gżejjer Maltin. NAO varjabbli hija parti minn ċiklu. Fi snin imgħoddija rajna xtiewi simili kemm il-darba. L-aktar magħrufa kien dawk ta’ 1990, 1996, 1998, 2000, 2009 u 2015. Din ta’ l-aħħar kienet rekord. Xjentisti skoprew xi ħaġa stramba ħafna, pero’. Il-varjazzjoni ta’ l-NAO saret aktar drammatika dan l-aħħar. Ma għadux possibbli tipprevjedi kif se tkun minn ħafna qabel. Jgħidu li n-nuqqas ta’ silġ fl-Artiku minħabba tibdil fil-klima qed iwassal biex l-Icelandic Low tidgħajjef. Dan ifisser li l-NAO tibda tkun fi stat pożittiv aktar spiss, u għalhekk se tiżdied il-frekwenza ta’ xtiewi sħan u nexfin fuq il-Gżejjer Maltin. Is-sjuf se jibdew ikun itwal u aktar sħan ukoll minħabba f’hekk. Ovvjament, ix-xitwa għad fadlilha xi ġimgħat, u l-NAO taf tinqaleb. Aktar ma’ jgħaddi ż-żmien, pero’, iċ-ċans li tinqaleb jonqos.