Area Forecast Discussion

KEY MESSAGES

Updated at 235 AM EDT Tue Sep 15 2026

- Scattered showers and thunderstorms focus mainly across Southwest Florida today. Frequent lightning, heavy rain and gusty winds will be possible with any storms. - An approaching upper-level low is expected to bring increasingly unsettled weather for the middle to end of this week. - High temperatures remain in the low to mid 90s across South FL each day, resulting in widespread Moderate HeatRisk.

SHORT TERM

(Today through Wednesday) Issued at 235 AM EDT Tue Sep 15 2026

The mid-week period consists of the formation of a Rex Block ridge that covers most of the central and eastern CONUS. In the western Atlantic, an upper-level low will be strengthening and advecting southwestwards underneath this ridge, which will effectively pull the low directly towards the Florida Peninsula given the where the ridge is located. While this upper-level low is not likely to reach our region until Wednesday night, we will still see the effects of it for this mid- week period.

Firstly, the pressure gradient will enhance as the low approaches in conjunction with the ridge strengthening. Latest HREF/LREF and other ensemble data suggests around a 70-80% chance that H500 heights will reach 600 decameters as a result of the amplifying ridge over the eastern U.S., which would be above the 90th percentile for heights. As a result, the pressure gradient will strengthen and lead to a period of breezier easterly to northeasterly winds beginning as soon as later this afternoon, but definitely for tomorrow. With the lack of a surface low forming, not expecting these winds to be overly strong, but they will be above average in breeziness. Secondly, forcing for ascent will increase via positive vorticity advection occurring towards South Florida, which will provide energy for the production of widespread showers and thunderstorms. Given the increase in northeasterly flow, we should see the brunt of activity focusing in SW Florida, but speed convergence and early diurnal processes is expected to result in some scattered showers and thunderstorms in SE Florida as well for today and tomorrow.

Overall, given the increasing amount of showers and storms that are expected to form across the region over the next several days, the primary concern will be for excessive rainfall flooding although the risk for this also doesn't seem that high. HREF LPMM generally highlights a high-end scenario around 4-5" in a short time frame (~2 hours) with 90th percentile QPF (a reasonable high-end) of 2-4" total over the next few days combined. Additionally, severe parameters (lapse rates, CAPE/DCAPE, shear, etc.) are relatively benign, although of course an isolated strong core remains possible to occur via max convergence of low level boundaries that are able to spark a more robust updraft. Nevertheless, this has a very low chance of occurrence so not expecting much of a severe threat here through the period.

High temperatures across the region will generally reach the low 90s still through mid-week, with some areas seeing max temps in the upper 80s. Overnight lows for Tuesday night will range from the low to mid 70s across SW Florida to the upper 70s and low 80s for the east coast metro areas.

LONG TERM

(Wednesday night through Monday) Issued at 235 AM EDT Tue Sep 15 2026

The stout 600 decameter H5 heat dome will finally begin to weaken and shift west for the latter half of the week. The main high pressure center will move west of the Mississippi by Thursday, with mid-level height falls occurring across Florida as and inverted trough begins to push west across the Gulf Stream. There is very good agreement amongst both ensemble and deterministic guidance that a cut-off upper low will develop on the southeast side of the ridge. This will occur as part of the upper level jet detaches from the main flow over the Great Lakes, creating a Rex Block pattern across the southeast, with deepening low pressure over Florida and persistent ridging over the Deep South. This shift in the upper level pattern will create much more unsettled weather across South Florida, with PoPs climbing above 80% each day through the end of the week.

Continued deep moisture (with PWATs above 2 inches) and increased forcing aloft should allow for scattered to numerous storms to develop across the region. While there is still some spread in the guidance, most ensemble QPF clusters are only showing about 1.5 to 2.5 inches of rainfall for the Thursday through Friday period. These amounts shouldn't result in anything more than a few isolated urban flooding impacts for low lying and poor drainage locations. At the surface, pressure gradients will relax across the region after Wednesday, knocking down ENE winds back to around ten knots. This should result in slower and more erratic storm motions, with development following outflow and boundary collisions. But with the upper low moving overhead, increased forcing may allow for a few training storms to hit the same area multiple times. As the low crosses into the Gulf over the weekend, there is also an indication that there could be some coastal convergence and pinned coastal storms. While not quite perpendicular to each other, winds at 500 and 700 mbs will be out of the SW, while winds at the surface will be out of the E to NE. This may lead to slow moving storms and enhanced moisture convergence along the Paradise Coast, which also happens to be where most ensemble QPF clusters show the highest rainfall amounts to be (although mostly offshore).

While more uncertain, there will also be an isolated threat of severe weather as the disturbance crosses the region. Some models are showing that 500 mb temperatures may drop into the -8 to -9 C range, within the 25th percentile for this time of year. This could result in some steeper lapse rates, allowing for some stronger cores to develop and for a low chance of hail and strong downburst winds. However, increased cloud cover may inhibit the amount of diurnal heating and instability that accumulates throughout the day, keeping the threat of strong storms more conditional and low confidence.

Overall, highs will remain in the upper 80s to low 90s across SoFlo, with lows in the 70s. Once the upper low ejects out to the west on Sunday, we should return to our more typical sea-breeze dominated wind regime, with scattered afternoon storms.

AVIATION

(06Z TAFS) Issued at 137 AM EDT Tue Sep 15 2026

VFR is expected to prevail for most of the period. VCSH/SHRA expected to develop after 13-14Z today with VCTS later this afternoon after 18-20Z. KAPF will see the most activity due to winds being out of the E/ENE, which will put KAPF at highest risk for on site restrictions. The winds at KAPF will also shift out of the west after about 18Z. With a disturbance approaching for later this week, SHRA/TS development overnight looks likely, especially across the east coast.

MARINE

Issued at 235 AM EDT Tue Sep 15 2026

Benign conditions continue today, but increasing winds and seas are expected to arrive Wednesday towards the end of the week as a disturbance approaches from the western Atlantic. For today, a gentle northeasterly flow is expected across the Atlantic waters with light to gentle winds in the Gulf shifting to the SW in the afternoon. Seas remain at 2 feet or less for today. For Wednesday, northeast winds will increase, becoming moderate to fresh over the Atlantic waters and fresh to strong for the Gulf waters. Additionally, seas are expected to rise to 5-8 feet in the Atlantic by late Wednesday with Gulf seas at 3-5 feet. Therefore, increasingly hazardous conditions for small craft will be developing over the next several days and may require an advisory. Other than winds and seas, an increased number of shower and thunderstorms are also expected.

BEACHES

Issued at 235 AM EDT Tue Sep 15 2026

The risk for rip currents will rise beginning on Wednesday and into the late week period as increased onshore winds and swell arrive due to a disturbance approaching from the western Atlantic. This risk is expected to remain elevated for several days.

PRELIMINARY POINT TEMPS/POPS

MFL WATCHES / WARNINGS / ADVISORIES

FL...None. AM...None. GM...None.