( ( Maritime ( tropical ( -LRB- ( mT ( -RRB- ( air masses ) ) ) ) ) ) ( ( ( move ( into ( the ( United States ) ) ) ) ( from ( over ( ( the Gulf ) ( of ( ( ( ( ( Mexico , ) ( the ( Caribbean Sea ) ) ) , ) and ) ( the ( tropical ( Atlantic Ocean ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Maritime) (JJ tropical) (-LRB- -LRB-) (NN mT) (-RRB- -RRB-) (NN air) (NN masses)) (VP (VBP move) (PP (IN into) (NP (DT the) (NNP United) (NNPS States))) (PP (IN from) (IN over) (NP (NP (DT the) (NNP Gulf)) (PP (IN of) (NP (NP (NNP Mexico)) (, ,) (NP (DT the) (NNP Caribbean) (NNP Sea)) (, ,) (CC and) (NP (DT the) (JJ tropical) (NNP Atlantic) (NNP Ocean))))))) (. .)))
Maritime tropical (mT) air masses move into the United States from over the Gulf of Mexico, the Caribbean Sea , and the tropical Atlantic Ocean.
(ROOT (S (NP (NP (DT The) (JJS best) (NN explanation)) (PP (IN for) (SBAR (WHADVP (WRB how)) (S (NP (NN air) (NNS masses)) (VP (VBP move) (PP (IN across) (NP (DT the) (VBN united) (NNS states)))))))) (VP (VBZ is) (SBAR (IN that) (S (NP (DT the) (VBG prevailing) (NNS westerlies)) (VP (VP (VBP move) (NP (NN air) (NNS masses)) (PP (IN from) (NP (NN west))) (PP (TO to) (ADJP (JJ east))) (PP (IN across) (NP (DT the) (VBN united) (NNS states)))) (CC but) (VP (MD may) (VP (VB be) (VP (VBN deflected) (PP (IN by) (NP (DT the) (NN jet) (NN stream)))))))))) (. .)))