Melbourne, Florida

New KEY MESSAGES, DISCUSSION, MARINE

• Later today, rain bands are expected to increase in coverage as a disturbance moves overhead. Through Monday, widespread rainfall of 1-3 inches is forecast with a 10% chance of 5-7 inches. Where soils are already saturated, a Flood Watch is in effect for Brevard, Indian River, St Lucie, and Martin Counties from 10 am today through Monday afternoon.
• Beach conditions remain dangerous today and Monday along Central Florida`s Atlantic coast. A High Surf Advisory remains in effect for 5-7 ft breakers, and there is a high risk of life-threatening rip currents. Please remain out of the ocean! Minor to moderate coastal flooding may occur at high tide mainly near and south of St Lucie Inlet.
• The combination of rough seas and fresh easterly winds continues to cause hazardous conditions for boaters, especially in the open Atlantic. A Small Craft Advisory is in effect through at least Tuesday morning.

-----------Synoptic Overview-----------

Early this morning, we are tracking a shortwave trough extending from the NE Gulf to the Missouri River Valley. This feature is on the nose of a subtropical jet segment emanating from the Four Corners to the Plains. At the surface, a 1035 hPa high-pressure system is centered near Philadelphia, PA. Brisk easterly flow continues in the boundary layer over Florida, courtesy of a tight pressure gradient to the south of the surface anticyclone. Copious moisture, with PWAT values exceeding 170% of normal, extends from the southern half of Florida into the northern Gulf.

Over the next 24 hours, the disturbance immediately west of Florida is forecast to move over the state. As this occurs, Central Florida will become positioned beneath a region of upper-level divergence, promoting synoptic-scale lift. This may also allow a diffuse surface trough to develop along the east coast of Florida. As the axis of deepest moisture centers itself over the peninsula, moisture convergence should become enhanced, particularly along the Atlantic coast. A weakly unstable environment is also anticipated, with MUCAPE values generally around 1250 J/kg or less. The ingredients for unsettled weather persist into at least Monday afternoon.

As the mid-level disturbance stalls over the area from late Monday into Tuesday, jet dynamics will become much less favorable for lift. However, plentiful moisture is forecast to remain in place through the middle of the week.

Quasi-zonal flow overtakes much of the U.S. later this week, with a pair of disturbances transiting the subtropical jet. We have been following these features in the guidance for a potential cold front on Thursday. Guidance has been trending weaker with the lead shortwave, and the 31/12Z ensemble suite continued that approach. For Florida, the secondary disturbance now provides the better chance for a diffuse cold frontal passage by Friday. This should allow some drier air to reach Central Florida next weekend, though substantial cool air advection is not expected.

Cluster analysis of the global ensembles indicates increasing model spread next weekend. Trough development is favored over the Southern Plains by around Sunday, with a reinforcing cold front possibly arriving by Monday the 9th. This front may have a better chance of delivering more autumn-like conditions to the area once it passes.

-------Sensible Weather & Impacts-------

Through Monday

The main concerns for the next couple of days are flash flood potential and hazardous coastal conditions across east central Florida. Here are some of the impacts...

Heavy Rain/Flooding

We`re already seeing some brief downpours early this morning, with bands of showers near Orlando and along the Treasure Coast. A moisture discontinuity lies between Daytona Beach and Orlando, with deeper moisture to its south. As the disturbance over the Gulf approaches, the environment will become increasingly favorable for rain bands, some of which are expected to become heavy at times. The greatest chance of this activity through sunset is generally from Brevard and Osceola Counties and points southward. By tonight, deeper moisture should overspread all of Central Florida, leading to additional development of showers and a few storms throughout the area. The high potential for numerous showers and locally heavy rain bands is expected to slowly diminish by Monday afternoon.

High precipitation efficiency within slow-moving rain bands may support locally intense rainfall rates. QPF clusters from the synoptic models, along with the latest REFS hi-res suite, suggest the heaviest rain potential is along the coast from Brevard County southward, perhaps extending into portions of Osceola and Okeechobee Counties as well. Antecedent conditions (recent rainfall) have left us with nearly saturated soils across nearly all of the Treasure Coast urban corridor. Coincident with this, we have issued a Flood Watch for Brevard, Indian River, St Lucie, and Martin Counties from 10 AM today until 3 PM Monday. This is where the greatest threat for flash flooding currently exists, but there is still a 5-15% chance of excessive rainfall across all of east central Florida over the next couple of days.

Admittedly, there is a lot of variance in the guidance, affecting confidence in exactly where the heaviest amounts will fall. All told, we still forecast widespread 1-3 inches through Monday night, with a reasonable worst case (10% chance) of 5-7 inches.

Thanks to WFOs Miami and Jacksonville for collaboration on this heavy rain and flooding threat.

Coastal Hazards

Persistent easterly winds gusting 20-30 mph continue to cause rough surf at all Atlantic beaches of Central Florida. A High Surf Advisory remains in effect for 5-7 ft breakers. Due to increased vulnerability caused by recent beach erosion, we have extended the High Surf Advisory through Monday for similar breaking wave action. Combined with the high risk of deadly rip currents, it is critical for residents and visitors to stay out of the ocean.

Minor to moderate coastal flooding remains a concern generally near and south of St Lucie Inlet during the afternoon high tides. If excessive rainfall occurs during high tide, flooding may be worsened due to impeded drainage into tidal waterways.

Tuesday - Friday

Onshore flow lingers on Tuesday, then begins to lessen on Wednesday. Ample moisture remains in place, but despite a nearby disturbance, the setup is less favorable for heavy rain. Still, we will keep a 50-60% chance for showers on Tuesday and a 30-50% chance on Wednesday. Areas that pick up heavy rain earlier in the week will still need to be monitored for localized flooding, mainly on Tuesday.

Statistical guidance has trended toward rain chances of 20% or less Thursday and Friday. As mentioned before, the initial cold front looks weaker, and the secondary boundary on Friday is rather diffuse, limiting convergence. Highs each day should range through the low to mid 80s with lows in the mid 60s to low 70s.

Next Weekend

Most likely, Central Florida will be in between weather systems next weekend. This should leave us with tranquil, pleasant conditions. We currently have a dry forecast with highs in the low 80s and lows generally in the 60s. It looks somewhat less humid as well.

Hazardous boating conditions will persist in the Atlantic waters off of Central Florida through early this week. A strong area of high pressure over the Northeast U.S. has tightened the pressure gradient, causing fresh easterly flow across the waters. Numerous showers and a few storms are forecast later today through Monday as a disturbance moves overhead. Winds slowly begin to slacken by late Tuesday and especially Wednesday, allowing seas to gradually subside by midweek.

The Small Craft Advisory continues for all of the local Atlantic through at least Tuesday morning, with the offshore zones remaining beneath the Advisory through at least Tuesday evening. East winds 15-25 kts through Monday, 15-20 kts on Tuesday, decreasing to around 10-15 kts by late Wednesday afternoon. Seas 5-9 ft through Monday, 5-8 ft on Tuesday, and slowly decreasing to 5-7 ft on Wednesday.

On and off showers/lightning storms are forecast through the TAF period with onshore flow. A TEMPO group for MVFR CIGs exists between 06Z-08Z at KMCO. TEMPO/PROB30 groups are likely to be added in the next TAF package for showers/storms late AM to PM SUN. Expect breezy E winds at 8kts-16kts w/ gusts to 18kts-25kts. MVFR CIGs are expected after 23Z at KMCO/KSFB/KISM/KLEE/KTIX.

DAB  80  71  79  71 /  50  80  70  40
MCO  79  69  79  70 /  70  80  60  40
MLB  80  71  80  71 /  80  80  80  60
VRB  82  71  82  71 /  80  80  80  70
LEE  81  69  80  68 /  60  70  50  30
SFB  81  70  79  70 /  60  80  60  40
ORL  80  70  79  71 /  70  80  60  40
FPR  81  72  81  71 /  70  80  80  70

FL

High Surf Advisory until 7 PM EST Monday for FLZ150-154-159-164-347-447-647-747.

Flood Watch from 10 AM EST this morning through Monday afternoon for FLZ154-159-164-247-254-259-264-347-447-547-647-747.

Coastal Flood Advisory until 7 PM EST Monday for FLZ159-164.

AM

Small Craft Advisory until 10 AM EST Tuesday for AMZ550-552-555.

Small Craft Advisory until 4 PM EST Tuesday for AMZ570-572-575.