A Coastal Flood Advisory is in effect for all of the Florida Keys. Key Messages:

• The combination of a higher-than-normal autumn spring tide (a.k.a. “king tide”) and the potential for locally heavy rainfall could result in street and low elevation area flooding tonight.

• The greatest threat for this combined flooding threat will be during the overnight hours tonight, generally between 9:00 pm and 5:00 Note that on the Bayside of the northernmost Upper Keys where the tide cycle is less distinct, the vulnerability to combined locally heavy rainfall and coastal flooding would be nearly continuous.
• Areas where king tide flooding is normally observed on dry weather days will be at the greatest risk for this combined rain-and-tide flooding. If heavy downpours occur during portions of tonight, streets in those areas may become impassable for a few hours at a time with the lowest elevation homes and businesses (those flooded by heavy rainfall alone in the past) may be impacted.

Situation:

A trough of low pressure over the Florida Keys will drift slowly westward over portions of the Florida Keys Thursday night. A more consolidated area of lower pressure is forecast to develop over the Florida Peninsula today through Saturday, then reforming closer to the Carolina coast later in the weekend. This weather pattern will likely keep higher than normal rain chances lingering into the day Saturday, before a more significant drying trend takes place Saturday night and Sunday.

If heavy downpours occur around the times of high tide, especially Thursday night and Friday night, the combination of little or no drainage may result in significant street and low area flooding at much lower rainfall rates than what would normally be expected for such flooding. Due to the lack of a distinct tide cycle on eastern Florida Bay and Blackwater Sound, the threat of combined tide and rainfall flooding would be spread throughout today through Saturday, with Florida Bayside coastal flooding likely only slowly subsiding through the weekend into early next week.

At this time, additional rainfall totals over the Florida Keys from now through Saturday are likely to range from 2 to 4 inches, with isolated amounts around 6 inches.

In addition, the Weather Prediction Center has outlooked the northernmost Upper Florida Keys (including Key Largo and Ocean Reef) for a marginal risk (Level 1 out of 4) of excessive (flooding) rainfall today and tonight.

The WPC Excessive Rainfall Outlook for Today and Tonight, indicating a MARGINAL RISK (Level 1 out of 4) for flooding rainfall from Plantation Key of Islamorada through Ocean Reef. 

This weather situation favors locally heavy rainfall with a risk for street and poor drainage area flooding, as the risk for severe local thunderstorms with damaging winds remains very low.

Timing:

The potential for locally heavy downpours coinciding with the high (king) tides will continue tonight.

Impacts:

Streets and low lying areas normally impacted by king tides during dry weather may become impassable for a few hours at a time with the lowest elevation homes and businesses (those that can be flooded by heavy rainfall alone in the past) also impacted.

Tropical Weather Situation:

Tropical Storm Jerry and Subtropical Storm Karen do not pose any threats to the Florida Keys. At this time, no tropical disturbances with any potential for impacts to the Florida Keys are being monitored for development over the next 7 days.

Next Update

The next update will be issued around 10:00 am EDT Saturday, October 11th.

You may contact the NWS Key West at (305) 295-1316 extension 3 to speak with a meteorologist 24/7.

Please contact us anytime if you require specific critical hazardous weather information for decision support in your agency, department or division’s activities.