Marine Weather and Tide Forecast for Port St. John, FL

DISCUSSION
Issued at 108 AM EDT Wed Jul 9 2025

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

Florida's weather continues to be strongly influenced by an area of deep-layer high pressure extending across the subtropics from the W Atlantic to the Desert Southwest. Tucked beneath the upper high is a weak wave of energy immediately northeast of the Bahamas. In the westerlies, a low-amplitude trough is pushing into the Ohio Valley.
Total moisture values are near normal for early July.

Over the next several days, little change to the synoptic pattern is forecast. The easterly wave in the Atlantic is expected to be redirected northward, generally not impacting local weather. Upper ridging remains firmly overhead. However, the weak trough well to our north may be enough to briefly oscillate the near-surface ridge axis toward South Florida on Thursday and Friday before it shifts slightly north toward Central Florida again this weekend.
Regardless, pressure patterns are loose; this suggests that the sea breezes should be able to form each day.

08/12Z ensemble cluster analysis continues to show a TUTT (tropical upper tropospheric trough) approaching the Bahamas sometime in the first half of next week. More importantly, several members also suggest that a well-defined mid-level wave will transit slowly westward across Florida. Coincident with this, the surface ridge axis is forecast to shift southward as moisture increases.

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

Today...

The overall setup is fairly unchanged from yesterday, and HRRR members seem to have high confidence in the evolution of scattered storms today. Aside from some isolated activity on the advancing sea breeze, we anticipate that the majority of showers and storms will be focused over the interior (50-60%) this afternoon and early evening, with lesser chances (30-50%) along the coast. Mid-level lapse rates look more impressive, leading to strong instability.
Brief wind gusts to 45 mph, frequent lightning, and torrential rain due to slow storm motions remain the primary threats. Seasonably hot and humid with heat indices reaching up to around 106 deg F.

Thursday-Weekend...

Surface high pressure slips a little farther south on Thursday and Friday, however, prevailing light winds will allow sea breeze formation each day. The focus of showers and storms looks a little closer to the coast and across South Central Florida on Thursday and Friday, with members now indicating somewhat drier air closer to the I-4 corridor.

This weekend, the surface ridge axis is forecast to return northward toward Central Florida. Seasonable coverage of afternoon and evening storms, mainly focused over the interior, can be expected.

Quick heating in the morning and early afternoon will allow heat indices to bounce up to as high as 106 deg F. Those working or playing outdoors should know the signs of heat illness and never leave children or pets in unattended vehicles.

Early Next Week...

A pattern change still appears to be favored as disturbances approach from the Atlantic, forcing the surface high southward while enhancing local moisture convergence. This should introduce higher coverage of showers and storms across Central Florida. This unsettled setup may last well into next week.

MARINE
Issued at 108 AM EDT Wed Jul 9 2025

Surface high pressure will remain over Central Florida and the adjacent Atlantic waters today before slipping toward South Florida late in the work week. While stronger storms should mostly remain over land, a few showers and storms are in the forecast, particularly in the overnight and morning hours. This weekend, the high shifts back toward Central Florida. The sea breeze should form each day, enhancing southeast winds at the coast. Generally favorable boating conditions persist.

Seas 1-3 FT through the weekend. Southerly-component winds (SE off the Treasure Coast, and more SW north of Cape Canaveral) up to 12 KT each day, turning onshore at the coast in the afternoon.

AVIATION
(06Z TAFs)
Issued at 108 AM EDT Wed Jul 9 2025

VFR conditions forecast through the early morning hours, with light and variable winds picking up out of the WSW after 15Z. The ECSB is forecast to develop and move inland late morning/early afternoon, with winds backing to out of the ESE along the coast and at all interior terminals except LEE. VCTS possible along the sea breeze, with greatest coverage focused across the interior after 20Z following the sea breeze collision. Have added TEMPOs at MCO, ISM, and SFB for MVFR conditions due to TSRA between 20-24Z. Activity is forecast to diminish after 02Z, with winds once again becoming light and variable at all terminals.

PRELIMINARY POINT TEMPS/POPS
DAB 90 75 91 75 / 60 40 60 10 MCO 94 76 93 77 / 60 40 60 20 MLB 90 76 91 76 / 40 20 50 20 VRB 90 73 91 73 / 40 20 50 20 LEE 91 76 92 76 / 60 50 50 10 SFB 93 76 93 77 / 60 50 60 20 ORL 93 76 93 77 / 60 40 60 20 FPR 90 73 91 74 / 40 20 50 20

MLB WATCHES/WARNINGS/ADVISORIES
FL...None.
AM...None.