Slow slide into fall

Wowsa! Am I lucky that I’m not writing for a Carolina crowd or I’d be pulling out my remaining hair. By sometime Sunday, we’re likely to see two Atlantic hurricanes, Humberto (now a tropical storm) and Imelda, which will form over the SE Bahamas. Imelda seems likely to threaten the Carolinas late Monday or Tuesday, but will be it be a frontal onslaught with flooding rains and surge, a glancing blow, or a close call? Turns out the answer will effect us in an indirect way and I’ll explain in “Long Range Ramblings.”

Closer to home, we’ll get a weak “cold” front through tonight. Tomorrows highs will still be in the upper 80s, but the humidity will be lower, and AM low temperatures should be mid 60s for Saturday and Sunday. Then, a warm up by mid-week which could feature our last 90 degree weather of the year (fingers crossed).

The Foreca graphic says it all. The rain is over. Skies should clear by morning and we’re faced with another dry week. So, it’s back to watering. Highs will be a bit cooler with 88 a reasonable value through Monday. Morning lows, however, will be mid 60s on the Northshore starting Saturday morning (maybe low 60s in interior areas such as Folsom and Bush). So it will be less humid with mornings meant for getting outside. Southshore lows still near 70.

A slight warm up back to the low 90s for mid week for what I hope is the last time this year. Then a cool down heading into next week which is based on a Carolina landfall of a hurricane. If that doesn’t happen, temperatures will hardly drop.

This IR satellite image shows a strong tropical wave producing several clusters of thunderstorms over Haiti and south of the Dominican Republic. This is the future Imelda which will emerge to the north of Haiti because the most recent thunderstorm cluster is happening there, showing where the convergence is moving towards. The tropical storm to the right is Humberto which should become a hurricane tomorrow.

Models are bullish on developing Imelda, all the way from a depression (late tomorrow just north of Cuba) to a small hurricane east of central Florida by late Sunday. There’s good reason for this - an area of light wind shear, an upper level high providing exhaust for the heat engine, and warmer than average sea surface temperatures. The arrows show the expected tracks.

We’re confident that Imelda will track up the East Coast of Florida (really, just offshore) because of the upper air trough with its westerly winds that will be over the Eastern Gulf (depicted by green arrows) tomorrow. The surface low will be in Alabama with the cold front (surface boundary between warm and cold air) trailing into the Gulf. Storms just don’t buck those winds aloft and cross those boundaries.

However, the real challenge lies on Monday when Imelda is east of Jacksonville. If Humberto were not there, Imelda would be drawn NNW at a slight angle into the upper trough and come in almost perpendicular to the South Carolina coast. That would be bad news for for them with heavy rains and surge. Indeed, our leading models, both the ECMWF and the American GFS depict this. However, that would be good news for us along the Gulf Coast as it would reinforce the northerly winds bringing in somewhat cooler air for late next week and next weekend.

But, Humberto is there, and it will be closer to Imelda on Sunday than it is now! Some models bring Imelda as far north as Georgia and then turn it out to sea because of Mr. Fujiwhara adding its rotating effect. So we can’t be 100% certain yet. My take is that with Humberto moving slowly, the effect of the trough will be more important so I think the Carolina landfall scenario is more likely.

For those of us who care more about the weather here than a hurricane over there….early October should feature decent mornings, without really being cool. Lows mostly mid to upper 60s. Highs mid to upper 80s with almost no rain. Markedly cooler weather (highs 70s, low 50s) will wait until sometime in mid-October.

After a showery Friday, the pattern is the same as in Louisiana.