What the forecast actually says — NWS Area Forecast Discussions, decoded into plain English.
Area Forecast Discussion · National Weather Service Jacksonville (JAX) · issued Friday, October 16 at 2:39 PM EDT.
Revised in 21 passages since the 9:03 AM discussion. See every revision.
Messages
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Isolated Thunderstorms are Possible Across North Central FL this Afternoon and Early this Evening.
Marine & Coastal Hazards this Weekend and Next Week. Dangerous Surf Zone Conditions - High Risk for Rip Currents & Rough, High Surf Developing by Saturday Evening. Wind Gusts of 30-40 mph at Coastal Locations from Saturday through Monday. Gale Warnings for All Atlantic Coastal Waters from Saturday Afternoon through Monday Night. Minor Tidal Flooding Along the Atlantic Coast, Intracoastal Waterway and the St. Johns River Basin. Significant Beach Erosion Possible at Area Beaches During Times of High Tide from Sunday through at least Tuesday.
Short Term
Afternoon surface analysis depicts a strong cold front extending from New England southward through the southern Appalachians and the lower Mississippi River Valley. Meanwhile, impressively strong high pressure (1046 millibars) for mid-October was building eastward from the Rockies towards the Plains states in the wake of this strong cold front. Aloft. stout ridging centered east of the Bahamas was extending its axis westward to our area, downstream of a potent trough that was digging southeastward from the Upper Midwest and Great Lakes region towards the Ohio and Tennessee Valleys. Latest GOES-East derived Total Precipitable Water imagery indicates that a seasonably dry air mass was lingering across southeast GA, where precipitable water were generally around 1.25 inches. Otherwise, deeper moisture was gradually advecting northward from the FL peninsula ahead of the approaching front, with precipitable water climbing to near or just above 1.75 inches across north central FL, while values elsewhere were slowly approaching 1.5 inches. A healthy cumulus field has developed across our area as moisture levels gradually increase, but shower development thus far remains just south of our area in Volusia County (along the developing Atlantic sea breeze boundary), with convection otherwise confined to the Gulf waters adjacent to FL's Nature coast, as well as the Gulf Stream waters adjacent to east central FL. Temperatures at 18Z have generally climbed to the mid and upper 80s, with dewpoints ranging from the low and mid 60s across inland southeast GA and the Suwannee Valley to the low and mid 70s along the northeast FL coast.
Enough moisture will advect across north central FL later this afternoon and early this evening for isolated to widely scattered showers and a few embedded thunderstorms to develop, mainly for locations around Lake George and Crescent Lake, with measurable rainfall chances generally confined to areas south of a line from Gainesville to Palatka to St. Augustine. Any showers or isolated storms that develop across north central FL should dissipate before the mid-evening hours, followed by increasing multi-layered cloud cover overnight.
Potent troughing aloft will dig into the southeastern states tonight, driving a strong cold front across southeast GA and Suwannee Valley during the overnight and predawn hours, with this front crossing north central and coastal northeast FL towards sunrise. A few showers or light sprinkles will be possible along or just behind the frontal boundary, with winds abruptly shifting to northwesterly during the predawn hours and becoming gusty from north to south towards sunrise. Lower stratus cloud cover will also overspread our region during the predawn and early morning hours on Saturday, and late arriving cold air advection will drop lows to around 60 for locations north of Waycross in southeast GA, ranging to the lower 70s for north central and coastal northeast FL.
Short Term
Strengthening Northerly Winds Tonight: Gusts to around 30-40 mph expected on Saturday through Sunday. Strongest gusts mainly for the coastal areas.
Coastal & Marine Hazards Increase This Weekend.
Strong frontal boundary will likely have already cleared our area by Saturday Morning, as cool and dry high pressure ridging quickly builds in from the west, ushering in both the coolest and driest airmass of the fall season so far. This airmass will also feature windy northerly conditions Saturday that will transition towards more of a northeasterly wind event on Sunday. Not expecting much in the way of rainfall/convection with the frontal passage, though Hi- Res guidance is highlighting at least some isolated shower potential Saturday over southern areas, mainly during the morning hours.
The main difference with this event compared to the previous onshore flow event will be the strength of the presssure gradient and therefore expected winds, as low pressure rapidly intensifying off the Carolinas and pulling away towards the northeast will tighten the gradient. Despite flow generally around 15-25 mph with gusts up to the 30-40 mph range, tidal influences will line up closer to a new moon cycle, and therefore not expecting as impactful of a coastal/river flood event at this time. However, the persistent flow and some remnant tides still trapped in some areas (especially upstream for the St. Johns River) could return flooding concerns, but not until after the short term period. With this forecast package, have begun High Risk for Rip Currents beginning Saturday Morning, in addition to Small Craft Advisories/Gale Warnings over area waters.
Saturday will be overall warmer than Sunday with overall decreasing clouds, and chances for a few isolated showers over southern areas as mentioned above. High temperatures will be mainly in the 70s, though some areas may see a high temperature overnight tonight due to the cold air advection. Low temperatures will have a larger discrepancy thanks to the onshore flow: Upper 40s to mid 50s are expected generally north and west of the coast and St. Johns River Valley, with upper 50s to low 60s south and east. Highs will struggle to get out of the 60s for many on Sunday, with just a few clouds inland and more maritime influenced clouds streaming onshore further south and east. Isolated to widely scattered showers may also make it to the immediate coastline at times on Sunday.
Long Term
Coastal hazards including tidal flooding, gusty winds, elevated rip risk and surf expected Monday through Wednesday.
Strong high pressure will remain oriented to the north and northeast through most or all of the long term period, driving a prolonged period of elevated onshore flow. Model guidance is generally more divided with respect to the behavior of both the upper low and surface low to our northeast towards mid to late week, though there is at least enough agreement with respect to the system lingering near the offshore Carolinas vicinity through at least the Monday/Tuesday time frame, which will keep the enhanced onshore conditions going to an extent. As expected, beach, marine, and river hazards are forecast to continue through much of the long term, with magnitude of coastal/river flooding impacts to be monitored over the coming days - though confidence is growing with respect to at least coastal flood advisory conditions for the St. Johns River and coast. Temperatures will remain generally below normal for long term period.
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