textproduct: Miami - South Florida

KEY MESSAGES

Updated at 335 PM EDT Fri Aug 21 2026 - Heat index values peak between 105-110 degrees today with a Heat Advisory in effect only for Miami-Dade and Broward counties.

- Scattered thunderstorms expected after midday and into the evening. A couple of stronger storms are possible that could produce near-severe winds.

UPDATE

Issued at 335 PM EDT Fri Aug 21 2026

Water vapor satellite imagery shows a moister air mass continuing to overspread South Florida today, with recent ACARS sounding data showing PWATs around 1.9 inches. Isolated showers and thunderstorms have begun forming this afternoon along the Atlantic sea breeze, which has remained pinned close to the East Coast under persistent southwesterly flow. High-resolution model guidance continues to show increasing coverage of showers and thunderstorms across the eastern half of South Florida and around Lake Okeechobee through the rest of the afternoon into the early evening, with outflow boundaries potentially driving some activity into SW Florida around sunset. Primary threats include gusty winds, frequent lightning, and localized heavy rainfall, though an isolated severe storm cannot be completely ruled out. Convection is expected to gradually dissipate following the loss of daytime heating after sunset. Overnight lows tonight will range from the low 80s along the coasts to the mid 70s inland.

SHORT TERM

(Today through Saturday) Issued at 116 AM EDT Fri Aug 21 2026

As the ridge in the Southwestern US continues to strengthen, increased jet dynamics will result in an amplified trough across most of the Eastern Seaboard through this weekend. The base of the trough is not anticipated to make it all the way to South Florida and the overall flow pattern will remain largely on the weaker side, but this enhanced troughing pattern is expected to keep a prevailing southerly/south-southwesterly flow pattern in place today and Saturday. Therefore, with abundant moisture advection continuing and elevated PWATs of 1.7-2.0" or even more in some areas, diurnal heating and sea breeze circulations each day will have the necessary ingredients to produce scattered to numerous showers and thunderstorms. With the primary south to south-southwest flow, this will favor interior and Southeast Florida for highest rain chances both today and on Saturday as showers and storms are expected to be the most widespread in these areas. Some activity will be observed across Southwest Florida as well, just not as widespread and thus rain chances are between 30-50% there versus 50-70% across Southeast Florida. Model soundings do highlight adequate SBCAPE of 3000-4000 J/kg as well as inverted-V signatures and steep low level lapse rates, so there will be an outside chance for an isolated severe storm or two via gusty winds. Otherwise, the primary hazards will be heavy rainfall that could lead to localized flooding in poor drainage areas, and sub-severe strong wind gusts.

High temperatures the next couple days will remain in the low to mid 90s. The deeper moisture will also keep dew points in the mid to upper 70s each day, thus maximum heat index values are anticipated to remain elevated up to the 105-110F range. Isolated locations could experience heat index values a couple of degrees higher for a short period of time. With the expectation of some increased cloud cover today and perhaps slightly lower dew points, it has been decided to only issue a Heat Advisory for Miami-Dade and Broward counties from 11AM - 6PM today. HREF probabilities currently indicate a 10% or less chance for heat indices to reach 108F or higher. Depending on how conditions are trending through the morning, a short-fused expansion of the advisory will be possible but is not imminent.

LONG TERM

(Saturday night through Thursday) Issued at 116 AM EDT Fri Aug 21 2026

As the trough draped across the Eastern Seaboard starts to erode early next week, the local wind regime will start to shift back to what we typically see in the summer time here in South Florida with low level flow being dominated by the Atlantic sea breeze. This will cause diurnal convection to start focusing back over both the interior and Southwest Florida rather than Southeast Florida like has been observed recently. Starting Monday, the highest rain chances (60-80%) will begin to focus across Southwest Florida and this will last through the end of the long term period.

Latest guidance shows some slightly drier air (PWATs falling back below 1.8-2.0") this weekend, which could result in some slightly lower dew points that end the current streak of consecutive days with Heat Advisories. There is also potential for another Saharan Air Layer (SAL) to impact the area late in the weekend and early next week, but guidance highlights this SAL breaking up upon it's arrival and thus it's influence on a return to hot conditions should be less than the previous round.

High temperatures are projected to remain in the low to mid 90s each day with overnight lows ranging from the low 70s across the interior and lake regions to the upper 70s and low 80s along the coastal metros.

AVIATION

(18Z TAFS) Issued at 127 PM EDT Fri Aug 21 2026

SHRA/TSRA will increase in areal coverage throughout the day with the potential for sub-MVFR cigs/vis at some terminals in tandem with erratic wind shifts. Onshore winds increase at all terminals this afternoon, then return to light and variable after sunset. TEMPOs and short-fused amendments may be needed with future TAF updates.

MARINE

Issued at 116 AM EDT Fri Aug 21 2026

Gentle west-southwest winds are expected across the Gulf waters today with southerly winds continuing across the Atlantic. The Atlantic winds will eventually become more southeasterly over the weekend. Seas will remain at 1-2 feet or less each day across all local waters. Scattered showers and thunderstorms are possible late each day and in the late night hours which may result in locally hazardous winds and seas.

PRELIMINARY POINT TEMPS/POPS

Miami 80 94 79 93 / 10 30 20 60 West Kendall 78 94 77 92 / 10 40 20 70 Opa-Locka 79 94 79 93 / 10 40 10 60 Homestead 79 93 79 92 / 10 30 20 60 Fort Lauderdale 80 93 80 92 / 10 30 10 50 N Ft Lauderdale 80 93 80 93 / 10 30 10 50 Pembroke Pines 80 93 80 93 / 10 40 10 50 West Palm Beach 79 94 78 94 / 10 40 10 50 Boca Raton 79 92 79 92 / 10 30 10 50 Naples 79 91 79 91 / 10 20 10 40

MFL WATCHES/WARNINGS/ADVISORIES

FL...Heat Advisory until 6 PM EDT this evening for FLZ071>074-172>174.

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