Key MESSAGE 1, High pressure and a relatively dry airmass will remain in place through the middle of the week, with temperatures forecast to be at, or just below, normal for early October. The drier airmass plus decent radiational cooling conditions may allow some inland locations to dip into the upper 40s tonight and possibly even again Wednesday night. Closer to the coast, high clouds skirting the area at times may prevent temperatures from getting as low as they otherwise could.
In addition to the lower temperatures, the decent radiational cooling conditions each night will probably favor a risk of fog development. At the moment, it looks to be more shallow in nature and not as impactful, but is something we'll continue to monitor.
KEY MESSAGE 2, Late this week and into this weekend, the upper level pattern will begin to change. Initially, an upper level ridge will briefly expand across the Southeast U.S. While dry weather will continue beneath the ridge, building low-level thicknesses should support warming temperatures, with highs flipping back to above normal. Most inland areas should manage to reach the low to mid 80s, with highs around 80 along the coast.
Over the weekend, and into early next week, the ridge is forecast to shift east into the western Atlantic. As this happens, it should help steer any Gulf tropical system north through the Gulf Coast States and into the TN/OH Valleys. East of that system, a warm front is forecast to lift northeast along the Southeast U.S. Coast on the leading edge of a plume of deep, tropical moisture. Of note, while a weak area of low pressure may develop along the northward-advancing warm front, the latest guidance has significantly backed off on the potential for a stronger low to develop. Should this trend hold, it would mean weaker winds and less coastal impacts. There is still a lot of uncertainty with the track and evolution of the Gulf system and the track once it moves inland.
For now, the main messaging focus is for a period of moderate to heavy rain on Sunday and Monday across ENC. Ensemble, deterministic, and machine learning guidance are well-clustered on a broad area of 1-2" of rainfall for the area. Of note, there is a smaller cluster of guidance that suggests amounts as high as 2-3", but for now that is a lower probability solution. It is worth noting, though, that the probabilities of exceeding 1" of rain have increased to 50-70% for much of the area. Guidance suggests minimal instability, but sometimes this type of setup can favor some shallow, rotating thunderstorms along the advancing warm front where southeasterly flow is enhanced.
00z Wednesday through Sunday Pred VFR conditions expected through the TAF period with light winds and generally clear skies. Refs and HREF probs for fog tonight is near zero but very good radiational cooling conditions will be in place and could see patchy shallow fog late. However, if fog does develop, impacts to aviation are expected to be minimal.
Outlook: The overall pattern is expected to remain mostly unchanged through the end of the work week. Outside of a MIFG/BR/FG risk each night and morning, mostly VFR conditions are expected to prevail. The next chance for widespread sub-VFR conditions comes over the weekend as tropical moisture moves north into the area from off the Gulf and Southwest Atlantic. Ra and potentially a TSRA risk looks to accompany the increased moisture as well.
Winds and seas continue to subside as gradients relax with high pressure building into the region. Have allowed the SCA for the southern water to expire late this afternoon. Ne wind will be around 10-20 kt with seas around 3-5 ft and up to 6-7 ft across the 20-60nm zones south of Hatteras tonight. Ne to E winds around 5-15 kt with seas around 2-5 ft expected for Wednesday.
Outlook: High pressure is forecast to build overhead for at least a couple of days with a weaker gradient and lighter winds. Consequently, seas should lay down to 2-3ft for all coastal waters. This will be shorter-lived, though, as the gradient is forecast to re-strengthen over the weekend as a front develops off the Southeast U.S. Coast. This front will eventually lift north as a warm front on Sunday as a tropical system in the Gulf lifts north through the Gulf Coast States and weakens. For now, at least, it now appears less likely that a secondary area of low pressure will develop along the advancing warm front. However, a period of moderate southeasterly winds is likely to accompany the front, with 20-30kt winds likely, along with seas building to 6-8ft at 7-8s. Stay tuned through the weekend as we continue to refine the potential marine impacts with this feature. A thunderstorm risk may develop with the weekend system as well.
Nc, none. Marine, none.
