* Storm Isaac could hit Florida coast by Monday * Top US growing state lost 50 mln boxes to storm in '05 * Nearby spread widens to January highs NEW YORK, Aug 22 (Reuters) - New York orange juice futures jumped almost 6 percent on Wednesday after U.S. forecasters warned Tropical Storm Isaac would strengthen into a hurricane and could hit the south coast of citrus-rich Florida by Monday. The National Hurricane Center said Isaac was strengthening in the Caribbean. Fears of damage to the country's top citrus-growing region pushed benchmark November frozen concentrated orange juice on ICE Futures U.S. up 5.9 percent to settle at a six-week high of $1.222 per lb. After finding resistance earlier in the day, juice futures punched through a 100-day moving average. On Tuesday, the half-a-billion-dollar orange juice futures market rose as much as 8 percent when forecasters cautioned about the strengthening tropical storm. September prices settled up 6.5 percent at $1.391 per lb, a three-and-a-half-month high and almost limit up. "This is all weather related. The path is looking like it'll hit Florida for sure," said Bill Collard, who heads up Florida-based commodity brokerage firm the Futures Management Group. Prices remained well below records of $2.2 per lb set in January when U.S. authorities restricted imports of Brazilian juice due to the use of a banned fungicide. Traders said they expected prices to remain elevated unless the storm veers away from the Florida coast. Still, market fundamentals are sluggish amid waning global demand and plentiful supplies, they said. "It probably should be going down because there's enough supply. (But) November could run to $1.30 before it finds some strong resistance," Collard said. Concerns about immediate supplies pushed September prices to a 17-cent premium over November prices -- the widest spread between front and second months since January when imports from Brazil, the world's largest producer, were restricted. Keener buying interest boosted September's Relative Strength Index (RSI) to 75, above the 70 threshold that signals overbought conditions and up from 68 on Tuesday. With five days until the storm is due to make landfall, Judy Ganes of commodity J. Ganes Consulting said buying could be overdone, leaving the market vulnerable to a sharp correction if the storm fades or misses Florida completely. Experts noted that frost and blight have done more damage historically to the Sunshine state's orange groves than hurricanes. The last storm to hit the state's southern farms was Hurricane Wilma in 2005, when some 40 million-50 million boxes of oranges were lost as the storm knocked fruit to the ground and damaged trees. To put that in context, that would be a third of Florida's estimated output for the upcoming marketing season which starts on Oct. 1, according to Bob Norberg, deputy executive director, research and operations at the Florida Department of Citrus. His calculation is based on recent private estimates. Measured against 2011/12 data, it would be about a quarter of the U.S. production. If that amount of production was lost now, the United States would have to double imports to meet its needs, Norberg said. Before Wilma in 2005, storms had not done substantial damage to Florida's crops since 1960 when Hurricane Donna hit. Even so, processors and producers, such as Coca Cola Co , which sells Minute Maid, and PepsiCo Inc, which has the Tropicana brand, fear getting caught short of supplies and paying meteoric prices for their raw material. They are able to pass on the cost to consumers, but that often leads to erosion in demand as households stop drinking juice, traditionally a U.S. breakfast favorite. Street prices shot up by almost a third in 2006 after Wilma's devastation, experts said. Any repeat of that could stoke worries about global food price inflation which are already heightened by soaring grain prices as the worst drought in half a century hit the U.S. corn belt.