It's not exclusive to Navarra, and it's not a denomination of origin. You can leave it in Spanish, I think, but I'd explain it by saying: "supurados,” a dried-grape wine /straw wine.

Here are some refs.

DESHIDRATACIÓN POR CALOR
• Elaboración. Los racimos vendimiados tardíamente son colocados a cubierto en zonas secas o quedan sujetos a la acción del calor artificial durante un periodo máximo de dos meses. Los racimos pasificados por la evaporación del agua poseen una elevada concentración de azúcar y son elaborados en el mes de enero siguiente, alcanzando una graduación de 18º.
• Nombre del vino y zonas. Recioto y amarone en la Valpolicella y passitos en distintas zonas de Italia, ***vin de paille (vino de paja)*** en Alsacia y Jura, tostadillos en España (prácticamente desaparecido en Pobla de Trives y Liébana, así como el ***“supurado”*** de Rioja ) y strobwein en Alemania y Austria.
http://elvino.paginasamarillas.es/magazine/articulo.asp?id=4...

Sweet wines can be informally categorized by the way they're produced. The key is to increase the sugar level. Most grape sugar converts to alcohol during fermentation. What's left is residual sugar (RS), which makes a wine taste sweet. RS by itself does not predict the perceived sweetness of the wine, because acidity also matters, but it's a good indicator.
Harvesting later. Leaving grapes on the vine to ripen further increases their level of sugar.
Example: Late harvest Zinfandel
***Drying. Grapes are dried by spreading them on mats or hanging them in a warm, dry attic. The moisture evaporates, turning them into raisins. The dried grapes contain more sugar than yeasts can ferment.***
http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2005/11/17/WIGA...

straw wine (sweet wine from grapes partially sun-dried on the vine or on straw mats)
http://wordnet.princeton.edu/perl/webwn?s=straw wine

The grapes looked great, and were immediately spread out in whole bunches on the drying racks under the trees in the paddock. These grapes were bought specifically to make ***dried grape wine or Vin de Paille (Straw Wine).*** If successful (and there are many areas of potential downfall) wine made from partially raisined grapes achieves a high degree of complexity and ages superbly. It is also the most ancient of winemaking techniques, used to ensure a high sugar concentration and therefore a natural stability and longevity.
http://tulbagh.com/TMV/february_2004.htm