J. Scott Applewhite / AP

Sen. Robert Menendez, D-N.J.

U.S. Sen. Robert Menendez this month wrote a $58,500 check to a company owned by a South Florida eye doctor and political fundraiser to reimburse him for two personal flights to the Dominican Republic that the New Jersey Democrat did not report on his Senate financial disclosure form, his office confirmed to NBC News Wednesday night. 

The disclosure came as law enforcement sources confirmed that FBI agents searched the West Palm Beach, Florida, offices of the doctor, Salomon Melgen, Tuesday night as part of an investigation that includes agents from the Department of Health and Human Services.

Melgen is a major Democratic political donor and fundraiser who together with family has contributed more than $200,000 to Democratic candidates, including $33,000 to Menendez. 

Menendez’s office confirmed that the senator — who this week became chairman of the Senate Foreign Relations Committee – wrote the check to Melgen from his personal account after aides reviewed his flight schedule in response to a complaint that a New Jersey Republican official filed with the Senate Ethics Committee last November. The complaint alleged that Menendez violated Senate Ethics rules by “repeatedly flying on a free jet to the Dominican Republic and other locations” and that the jet was provided by Melgen. 

“This was sloppy,” Dan O’Brien, Menendez’s chief of staff, told NBC News about Menendez’s failure to pay for the two 2010 flights at the time. “I’m chalking it up to an oversight.” Asked whether the senator has been contacted by the Senate Ethics Committee about the matter, O’Brien responded: “We can assume the Senate Ethics Committee is looking at the allegation. ”

O’Brien provided new details about Menendez’s relationship with the Florida doctor amid a swirl of media reports about the FBI probe. He said Menendez and the doctor have been longtime personal friends and that the senator has visited Melgen at his home in the Dominican Republican “about twice a year,” including attending Melgen’s daughter’s wedding. He said Menendez has generally flown commercial for those flights and paid for them out of his own pocket.

He confirmed that Melgen has also been an active fundraiser for Menendez, holding events for him at his home in South Florida as well as at a home he owns in Caso de Campo, a Dominican resort.

All told, the senator took three flights aboard Melgen’s jet in 2010 — one of which that May involved a trip to Puerto Rico and the Dominican Republican for political fundraisers, O’Brien said. One of those fundraisers was at Melgen’s home in the Dominican Republic, O’Brien said. The May 2010 flight for fundraisers on the two islands was paid for at the time by the Democratic Senatorial Campaign Committee, which Menendez then chaired. 

But after the ethics complaint was filed Nov. 3, his aides conducted what they described as an “exhaustive review of Menendez’s schedule” and found that the senator had taken two additional flights aboard Melgen’s corporate jet. One, from Aug. 6 to Aug. 9, 2010, was from south Florida to the Dominican Republic and back to south Florida. Another was from Sept. 3 to Sept. 6, 2010, was from Teterboro Airport in New Jersey to the Dominican Republican and back to New Jersey. In at least one of those flights, Menendez brought along guests, O’Brien said.

O’Brien said that after the review — spurred by the ethics complaint — Menendez wrote the $58,500 to Melgen’s company from his personal account. Under Senate ethics rules, senators are allowed to accept gifts from personal friends, but any valued at more than $250 must be publicly reported and approved by the Senate Ethics Committee.

In a statement earlier Wednesday, Menendez’s office said that: “Dr. Melgen has been a friend and political supporter of Senator Menendez for many years. Senator Menendez has traveled on Dr. Melgen’s plane on three occasions, all of which have been paid for and reported appropriately.”

That statement made no reference to Menendez paying for the trips in January, two months after the ethics committee complaint was filed. Asked about the omission, a spokeswoman for the senator said: “There was never any intention to be misleading.”

The spokeswoman said the senator was not aware of any time requirement for reimbursing for personal trips. She also said Menendez, by reimbursing for the flights, was not claiming the trips aboard Dr. Melgen’s plane was a personal gift. Although personal gifts above $250 need ethics committee approval, Menendez was not claiming the flights as a gift  and therefore does not need to seek approval of them from the committee, the spokeswoman said.

Updated at 11 p.m. ET: Tropical Storm Isaac strengthened on Friday as its lashing rains took aim at flood-prone Haiti, but it was not expected to become a hurricane until it barreled into the Gulf of Mexico early next week. 

On its current path, forecasters said Isaac would hit Cuba and the southern tip of Florida before making landfall anywhere from the Florida Panhandle in the northwestern part of the state to Alabama and as far west as New Orleans.

Forecasters put the entire coast of south Florida under tropical storm watch as of 5 p.m. EDT (2100 GMT) on Friday.

But the biggest immediate concern was heavily deforested Haiti, where the U.S. National Hurricane Center (NHC) said the full force of the storm was expected to be felt later Friday.  

Isaac could pass near Florida's Gulf Coast early Monday just as the Republican National Convention is scheduled to start in Tampa. 

Winds at tropical storm strength extend 185 miles out from Isaac's center, the U.S. National Hurricane Center said in an afternoon advisory, making it a very wide storm.

On exiting Haiti, Isaac's center should cross Cuba on Saturday, and then pass south of the Florida Keys before making landfall as a Category 1 hurricane overnight Tuesday somewhere between New Orleans and Tallahassee, NBC meteorologist Al Roker said Friday on TODAY. Warm waters in the Gulf of Mexico will be "energy for the storm" as it makes its way across the gulf, he added.

In related developments Friday:

• The U.S. embassy in Haiti sent an e-mail to American citizens in the country warning that flights into and out of Port-au-Prince have been suspended due to Isaac.
• Oil and gas producers in the Gulf of Mexico started preparing as Isaac's track looked to skirt the heart of the U.S. offshore energy producing zone. BP said it would shut down its giant Thunder Horse platform, the world's largest. Royal Dutch Shell, Chevron and Apache Corp. said they would evacuate some workers from their Gulf platforms with no production impacts. Other offshore drillers were likely to shut production in coming days as the storm approaches.
• The U.S. military moved 22 F-16s from Homestead Air Reserve Base in Florida to Fort Worth, Texas. Three F-15s from the base are on alert to move to Jacksonville if necessary.

South Florida could see a few twisters and heavy rain -- some 5-10 inches Sunday and into Monday, weather.com experts said in an online chat with readers Friday.

Florida has not been hit by a major hurricane since 2005 and officials are concerned that residents there have become complacent.

Aid workers prep Haiti's tent city residents for Isaac's onlsaught

"I think it's a challenge of getting people to understand their risk and make sure they’ve got a plan," said Craig Fugate, administrator of the Federal Emergency Management Agency.

With more than 19 million people living across the Sunshine State, Fugate wants every Florida resident to have enough supplies to last 72 hours and to know when to evacuate.

Click this image to get to our Atlantic storm tracker.

"I think the most dangerous thing is when people keep waiting to see what the next forecast is even if they’re in an evacuation zone. They say, 'Oh, it’s just a Category 1 storm or a minimum hurricane.' We’ve seen significant impacts from tropical storm force winds and rain," Fugate added.

In the Florida Keys, where there are few routes available for evacuation -- U.S. 1, Key West International Airport, and the Florida Keys Marathon Airport -- Mayor Craig Cates said his biggest concern was the storm's timing. Cates said he would need at least 36 hours to begin evacuations of tourists and residents.

"If it (Isaac) comes straight on to Key West, we’re worried about the damage that could happen in Key West. If it goes further up the Keys, it could damage power lines and we could get affected," Cates said. "Even if it hits further up the state, we have got to be prepared with our generators and our supplies. Being on an island, we understand that."

Forecasters with The Weather Channel think the evacuation decisions could come quickly. It is anticipated that watches will be issued for South Florida and the Keys by Friday night. In the event of an evacuation, Cates told The Weather Channel that tourists would leave first, followed by special needs citizens. 

Live updates and analysis from weather.com
Transcript of weather.com experts answering Isaac questions 

Florida Gov. Rick Scott said state officials are working with convention organizers, who will ultimately make the call on a delay or cancellation of the event.

State officials announced Thursday that they will wait to make decisions about moving supplies until after Isaac passes Cuba. FEMA has already placed food and generators in Jacksonville.  

Isaac is forecast to remain a tropical storm after crossing the Dominican Republic and Haiti and then passing over Cuba into the Florida Straits.

The National Hurricane Center warned it was "important not to focus on the exact track because of forecast uncertainties and the fact that Isaac has a large area of tropical storm force winds."

Follow Isaac's path with our storm tracker

Isaac was expected to dump between 8 and 12 inches of rain over parts of Haiti and the Dominican Republic, and up to 20 inches in a few areas. That poses a significant threat to Haiti, which is highly prone to flooding and mudslides because of its near-total deforestation.

Haiti, the poorest country in the Americas, still has about 350,000 people living in tents or makeshift shelters more than 2-1/2 years after a devastating earthquake that took more than a quarter of a million lives.

Red Cross workers toured crowded tent camps of Haitians left homeless by the 2010 quake to warn about Isaac.

Authorities in the Dominican Republic evacuated people living on the banks of rivers, streams and areas vulnerable to landslides in preparation for the approach of Isaac, whose effects were beginning to be felt with showers in the south of the country.

Weather.com and Reuters contributed to this report.

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