Browse Month

September 2010

Mid-Atlantic Discussion – September 22

WARNING: Technical discussion.

While there is a cold front approaching the area from the NW, the overall synoptic setup leaves much to be desired. The main player for severe weather today will be weak mesoscale forcing along with the cold front, which is visible this morning as lines of showers drape NE-SW over central OH, western PA and additionally over the southern Appalachians. Synoptically, a large area of high pressure moving off the coast leaves behind plenty of dry air in the region.

Upper-level forcing remains weak in our area as the jet stream remains well to our north. The jet could provide enough upper-level divergence for a small tornado risk in NoPA/EaPA and in NoNJ and SoNY, but speed shear will be weak further south. There is marginal directional shear in the lower levels throughout the region, but flow remains unidirectional in the mid and upper levels.

Steep low-level lapse rates will aid in creating strong outflows from mature storms, some of which could get to the severe level. CAPE and LI values are good, but dry air near the surface could hinder TCUs from forming. Storms that do form will largely be pulse-type, with isolated bowing cells possible.

All-in-all, I would expect today to perform much like the severe weather events we experienced early in the summer, which led to an under-performance based on the SPC outlooks. The severe threat in areas south of I-80 in central PA will be marginal at best.


—–

Chase potential: 25%

Chase target(s):
EaPA/NJ

Drought cancel coming up for the East Coast?

With the models starting to get a consistent idea that heavy rainfall will be possible along the East Coast next week, could the drought-stricken coast have a sudden end to this summer’s dry run?

The GFS model is much more bullish than the ECMWF model when it comes to rainfall… it has a slightly slower tropical system with a track that’s further west than the ECMWF. Most of this tropical precip. north of VA comes in the 11-15 day period in the GFS. Both models show that, between the cut-off low and the tropical system, widespread 1-2″+ rainfall totals are possible throughout the Mid-Atlantic and northern Southeast during the 6-10 day peroid.

NOTE that the GFS 00Z images below are very bullish. Images are courtesy of MDA/EarthSat.

GFS 6-10 day precip totals:

GFS 11-15 day precip totals:

Current drought conditions:

T.S. Lisa in the E. Atlantic… Activity picks up in the Caribbean

Tropical storm Lisa formed in the East Atlantic yesterday as an area of interest begins to organize in the eastern Caribbean. Lisa is expected to meander around the East and Central Atlantic while remaining far away from the U.S., but the disturbance in the Caribbean has been forecast by the models to have a chance at a U.S. landfall. Beyond that information, there won’t be much to report on the potential system until it develops into a tropical cyclone and begins a definitive motion. There’s still a wide range of possibilities out there, so anyone who says “it will hit X” in the next few days is talking complete bull.

Tonight, Jason and I will be attending the first DC AMS meeting of the 2010-2011 chapter year. Jason will be live streaming the meeting on his site, and I’ll be the tired guy pretending to be fully conscious.

What to Watch Fore(cast) – Sep 20-26

Highlights:

The calm before the storm – This week remains relatively quiet in the tropics as the focus moves to storm formation in the Caribbean. The models are strongly suggesting that the 11-15 day period could be memorable for the U.S. (see the post from 9/19).

The heat continues – The eastern U.S. will be getting very warm temperatures this week, with the warmest temperature anomalies shifting into the western U.S. by the end of the week.

Continual rain in Texas and the Desert Southwest – Rain will be ongoing through most of the week in Texas and parts of the Desert Southwest as an upper-level trough brings a storm system into the region during the second half of the week.

Storm systems slam into the Pacific Northwest – A series of low pressure systems will bring lots of rain and cloud cover to the Pacific Northwest, especially for areas near the coast.

—–
Discussion:

As Igor and Julia move off to the east and while anything that forms in the East Atlantic this week will stay well to our east, we can take a collective breath before next week’s forecast develops a tropical system or two in the Caribbean. The models have been consistent with developing a storm in the Caribbean that could make landfall on the U.S. in 2-2.5 week’s time. Updates will come as things become clearer.

The eastern U.S. will get a blast of heat over the next few days as a ridge of high pressure in the Southeast draws warm air up into the Mid-Atlantic and Northeast. This heat will subside back to normal temperatures over the weekend as a cold front moves into the Southeast. Parts of the Northeast could receive a good amount of rain from this late-week system, but most of the Mid-Atlantic is supposed to miss out of the much-needed precipitation.

The heat will shift towards the west as an upper-level ridge builds over the region going into the weekend. This burst of heat will bring summer back into the region as we begin the first week of fall, which starts on Wednesday. This heat will be temporary as an upper-level trough pushes into the Pacific NW next week and the ridge shifts back to the east.

Texas and parts of the Desert Southwest will get daily rainfall through mid-week as monsoonal moisture and a low pressure system approaching from the west bring a decent amount of precipitation to the region. Further north in the Pacific Northwest, low pressure systems continue to roll into the region off of the Pacific, bringing clouds and rain into the region throughout the week. The southern and eastern extent of this rainfall will be cut-off not too far inland as the ridge builds into the region over the weekend, but the West Coast could see significant amount of rainfall of 1-4+ inches if the moisture arrives as expected.

Igor bears down on Bermuda as we look into the future

Igor is currently a category 1 hurricane with sustained winds of 85 mph as it slams Bermuda with tropical storm force winds this morning. Don’t let the weakening in wind fool you… the swath of hurricane and tropical storm force winds is so vast that Bermuda will be inundated by Igor for a good 24 hours from the beginning of the event before tropical storm conditions will subside. This is quite a long time for those in the way of a tropical system. Good luck to all those out in Bermuda weathering the storm.

Looking into the future, another tropical wave is trying to form into a tropical system just off the coast of Africa, but this storm is forecast by the models to stay very, very far off to the east. The next real threat to the U.S. could form in the western Caribbean about 8-10 days from now. Both the GFS and ECMWF models have something forming in that area, but the upper-level pattern which would steer the storm is nearly the opposite in the 11-15 day period between these two models, which would greatly affect where this potential storm could make landfall. The only reason why I mention a storm this far out is because of the consistency the models have shown in developing a system in the Caribbean during this time frame, and it stands a chance of making a U.S. landfall. I will continue to monitor the situation with this system, but it remains so far out into the forecast that nothing can be certain.

Karl makes landfall in Mexico as a major hurricane

Major Hurricane Karl broke Bay of Campeche records for being the strongest hurricane that far south into the Bay. Karl came off of the Yucatan Peninsula as a Tropical Storm and quickly spun up over the course of 1.5 days to a category 3 winds, eventually maxing out at sustained winds of 120 mph.

Here’s the official data:

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL132010
1200 PM CDT FRI SEP 17 2010

…KARL MAKES LANDFALL ON THE SOUTHWEST GULF COAST OF MEXICO…

MEXICAN RADAR OBSERVATIONS AND SATELLITE IMAGES INDICATE THAT THE
CENTER OF HURRICANE KARL MADE LANDFALL ON THE SOUTHWEST COAST OF
MEXICO ABOUT 10 MILES…15 KM…NORTH OF VERACRUZ MEXICO NEAR 1130
AM CDT…1630 UTC. THE MAXIMUM SUSTAINED WINDS AT LANDFALL WERE
ESTIMATED TO BE 115 MPH…185 KM/HR.

SUMMARY OF 1130 AM CDT…1630 UTC…INFORMATION
————————————————–
LOCATION…19.3N 96.2W
ABOUT 10 MI…15 KM N OF VERACRUZ MEXICO
MAXIMUM SUSTAINED WINDS…115 MPH…185 KM/HR
PRESENT MOVEMENT…WSW OR 255 DEGREES AT 8 MPH…13 KM/HR
MINIMUM CENTRAL PRESSURE…976 MB…29.82 INCHES

Initial readings near the core reported weaker winds when the eye came ashore around 12:30pm EDT, so further analysis will have to be done for sure. It was definitely a unique and interesting hurricane.

Mid-Atlantic Discussion – September 16

A shortwave trough will be packing a big punch of energy as it moves east over the Mid-Atlantic region. In the high shear/low CAPE category, this system has plenty of upper-level support from a vort. max and the left-exit region of a developing upper-level jet. A strong 850mb jet will also be developing this morning and afternoon, which will provide nice bulk shear values in WV and W PA. This low-level jet will also rapidly transport 60s dewpoints into the region, which will help fuel storms as they initiate west of the Appalachians.

Visible satellite and radar looks rather poor this morning, with widespread cloud cover and precipitation in OH, WV and W PA. However, given the good amount of upper-level support and orographic lift from the Appalachians, storms could still fire soon after the rain passes through. Water vapor looks favorable for dry-slot initiation, which can be rather potent with the upper-level support. This would lead me to generally agree with the SPC forecast with the overall severe risks.

There is also a risk for severe weather near the East Coast as unstable air moves in off the Atlantic, but it will not have as much support from the upper-level features, so it will have to rely more on daytime heating to initiate storms.

—–

Chase potential: 60% (would be higher if travel distance was shorter)

Chase target(s):
WV/W PA
DELMARVA/NJ