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Vortex–vortex interaction between Hurricane Nadine (2012) and an Atlantic cut‐off dropping the predictability over the Mediterranean
Author(s) -
Pantillon Florian,
Chaboureau JeanPierre,
Richard Evelyne
Publication year - 2016
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.2635
Subject(s) - climatology , extratropical cyclone , peninsula , landfall , mediterranean climate , tropical cyclone , trough (economics) , vortex , typhoon , precipitation , predictability , environmental science , mesoscale meteorology , cyclogenesis , geology , meteorology , cyclone (programming language) , geography , physics , quantum mechanics , field programmable gate array , computer science , computer hardware , archaeology , economics , macroeconomics
Operational ensemble forecasts for the western Mediterranean exhibited high uncertainty while Hurricane Nadine was moving slowly over the eastern North Atlantic in September 2012. The forecasts showed a bifurcation in the track of Nadine —a significant fraction predicting its landfall over the Iberian Peninsula—and a high spread in the synoptic conditions downstream. The forecast uncertainty was a major issue for planning observations during the first special observation period (SOP1) of the Hydrological cycle in the Mediterranean eXperiment (HyMeX). Clustering the ensemble forecast of the European Centre for Medium‐Range Weather Forecasts reveals two scenarios for interaction between Nadine and an Atlantic cut‐off, which controls both the track of Nadine and the synoptic conditions downstream. The observed scenario of weak interaction is characterized by Nadine moving westward and the cut‐off moving eastward. The cut‐off then triggers precipitation over the Cévennes in southeastern France. The contrasting scenario of strong interaction is characterized by Nadine and the cut‐off rotating around each other over the Atlantic. Nadine then either merges with the cut‐off or makes landfall over the Iberian Peninsula. The interaction between Nadine and the cut‐off mimics the vortex–vortex interaction previously observed between two tropical cyclones or two upper‐level vortices. It differs from the usual interaction between a tropical cyclone and a larger trough during extratropical transition. A critical distance of about 1000 km between Nadine and the cut‐off distinguishes between the cases of weak and strong interaction in the ensemble forecast. Shifting the initial position of Nadine in Meso‐NH numerical experiments confirms the critical distance and suggests a bifurcation point in the relative position of Nadine and the cut‐off. The high forecast sensitivity to the vortex–vortex interaction resulted in the lowest predictability over the Mediterranean during the whole HyMeX SOP1.