Wednesday, October 5, 2005

Tammy Tell Me True

All eyes are on minimal Tropical Storm Tammy today for the chance to bring us some drought-breaking rain. But first, let's clear up the October Urban Legend. It may be because perfect warm, dry days like today are so memorable that it seems as if October is usually a dry month. In fact, October is a transition month between the normally wetter summer and the normally drier winter. The record shows that October has only the 7th driest long-term average rainfall of all the months of the year in Washington DC weather history. That's right, at 3.22", October is (just barely) wetter than January's 3.21". The driest month is February, with 2.63". Of course, February also has only 28.25 days on average, but even accounting for that, October is nearly 12% wetter than February. The months which have less total precipitation than October are: January, February, April, June, November, December.

Currently, temperatures are near or even a little above 80 in the metro area under sunny skies.

Tonight and Tomorrow

Tonight should see lows in the low 60s with increasing cloudiness toward morning. Tomorrow will be mostly cloudy with highs in the upper 70s.

Tropical Beat

Tropical Storm Tammy developed just off the Florida coast this morning. This is only the 4th time there has been a 19th "named" storm in a single year, and it is the earliest one by almost 3 weeks. The others formed on 12/07/1887, 10/25/33, and 10/27/95 ("Tanya").

At 2pm, Tammy was centered only 20 miles northeast of Daytona Beach, moving north-northwest at 14 mph. By the 5pm advisory, it was 15 miles north-northeast of St. Augustine. Maximum winds had increased slightly to 50 mph, but tropical storm winds extended as much as 260 miles from the center. The strongest winds and heaviest rains were mainly to the north and east.

On the forecast track, the storm should be a depression in central Georgia by tomorrow evening. That's when things start to get interesting for us. There is a lot of moisture associated with this storm, and indications are that it will be moving northeastward as the high pressure ridge now over us moves slowly eastward off the coast. The global forecast model ("GFS") from this morning's data has some light rain reaching the area as early as tomorrow afternoon, but the heavier amounts don't arrive until Friday morning. The latest model ("NAM") output from this afternoon's data delays the arrival of precpitation until midday Friday and keeps the heaviest amounts in eastern North Carolina and central Virginia. The official NWS precipitation forecast ("QPF") made early this afternoon has 2" to 3+" of rain in the local region for the 24 hours from tomorrow evening through Friday evening.

At this point, I don't have a lot of confidence in either the exact timing or the amount of rain, but this is the best chance we've had in at least about 6 weeks to get some serious precipitation in the Washington area. Stay tuned tonight and tomorrow for updates as the situation develops.

No comments:

Seasonal Outlook

Latest seasonal forecast: Click here.

Latest 3-month temperature outlook from Climate Prediction Center/NWS/NOAA.