Rainfall – September 29/30, 2015

Widely scattered showers, producing light to occasionally moderate rainfall moved across the area from late Tuesday to early on Wednesday.  The heaviest precipitation fell across southern Blaine County and western Canadian County, where radar rainfall estimates approached 1/2 inch.

The highest CoCoRaHS observation in the state came from OK-BL-1 / 9.8 WNW Geary with 0.14 of an inch.

Non-CoCoRaHS rainfall across the area included 0.08 of an inch at the Watonga Mesonet site, and 0.01 of an inch from the cooperative observer in Enid.

Major Hurricane Joaquin

…Hurricane Joaquin has rapidly intensified over the last 24 hours to a major hurricane…

…Imminent danger to the Bahamas / Concern increasing for the east coast of the U.S…

At 10 pm this Wednesday evening, Hurricane Joaquin was located about 90 miles east of San Salvador, Bahamas.  Air force Reserve Hurricane Hunter aircraft indicate that maximum sustained winds have increased to 115 mph, and Joaquin is now a major / category 3 / hurricane.

Model guidance is in reasonably good agreement that the storm will move slowly southwest over the next 24 to 36 hours, bringing dangerous hurricane conditions to the following locations:

* Central Bahamas including Cat Island, the Exumas, Long Island,
Rum Cay, and San Salvador
* Northwestern Bahamas including the Abacos, Berry Islands,
Eleuthera, Grand Bahama Island, and New Providence, but excluding
Andros Island and Bimini

Joaquin is expected to turn toward the northwest and north Thursday night or Friday – and this is when the forecast turns tricky.

A strong band of mid-level winds currently extends from the Northern Rockies to the Central Plains.  This jet segment is forecast to nose into the deep south, and eventually lead to a cut off low in the vicinity of southern Alabama by Friday afternoon.  Most reliable guidance points to an interaction between the cutoff low and Joaquin, with an evolution that slings the hurricane northwestward and eventually westward into the Carolina coast. Should this scenario play out, the potential exists for a variety of dangerous weather – especially near and north of the eye location.  The 18z GFS suggests that the westward movement of the hurricane will accelerate late Saturday and early Sunday.  A quick westward motion would mean that the system will still be quite strong well inland, meaning an increased area of damaging wind potential.  Of possibly greater concern would be flooding.  Much of the Carolinas and Virginia have been experiencing flooding, and numerous flood and flash flood watches and warnings are currently in effect.  The amount of rainfall that a hurricane would bring could lead to catastrophic flooding.

Now to the biggest forecast issue.  The ECMWF is and has been forecasting Joaquin to stay well offshore, with very little impact to the east coast.  This is important because the ECMWF has proven to be a very reliable model when it comes to tropical storms and hurricanes.  It is best known for its handling of Hurricane Sandy in 2012.

From the latest discussion from the National Hurricane Center:

Confidence in the details of the forecast after 72 hours remains
low, since we have one normally excellent model that keeps Joaquin
far away from the United States east coast.   The range of possible
outcomes is still large, and includes the possibility of a major
hurricane landfall in the Carolinas.

A hurricane watch for a portion of the U.S. coast could be
required as early as Thursday evening.

Tropical Storm Joaquin

Tropical Storm Joaquin was located about 405 miles east of the northwestern Bahamas at 4 pm this Tuesday afternoon.  Satellite imagery shows that strong shear which has been affecting the storm was beginning to relax, and the storm has responded with steady intensification.  The National Hurricane Center now expects the storm to become a hurricane within 24 hours as it moves slowly west southwest.  Tropical storm conditions could reach the Bahamas by Thursday morning.

Current model guidance is very supportive of Joaquin moving slowly west southwest over the next 48 hours.  Beyond that point, there is an extreme range of guidance that is literally thousands of miles apart in some cases.  The official forecast calls for the storm to turn north or north northeast on Thursday and accelerate – while tracking about midway between the North Carolina coast and Bermuda.  Beyond 48 hours, confidence in any forecast or model solution should be viewed as low.  At this point, anyone from the Bahamas and Bermuda to the east coast of the United States should keep a close watch.

Outlook (Monday-Wednesday)

…Cooler and drier air arriving on Wednesday…

Only minor differences between model guidance this Sunday evening.  An upper level low pressure area over south Texas will move slowly northeastward, phasing with a trough over the eastern U.S. by Wednesday.  An upper high over the southwest U.S. will make a half-hearted attempt to build toward the Plains, but will eventually flatten as a wave tops the ridge and moves southeastward toward Oklahoma late on Wednesday.

Showers near the western periphery of the Texas low will be possible across southeast Oklahoma on Monday and Tuesday.  Attention then turns to a cold front that will be pushing south across the Central Plains.  This front will begin to settle southward across the state late on Tuesday or early on Wednesday.  Cooler and drier surface air will begin to flow into the state on easterly winds during the day on Wednesday.

The approach of an upper wave in northwest flow, and low level upslope flow is expected to generate scattered showers and thunderstorms across the Central High Plains on Wednesday.  This precipitation will move southeast and reach northwest Oklahoma during the late afternoon and evening hours.  The rain is not expected to be particularly heavy, but some places could see upward of 1/3 inch.

Current thinking is that measurable precipitation will stay northwest of central Oklahoma.

…Hazards…

No significant weather related hazards.

…Okarche Weather…
Monday morning (Midnight to Noon):
Low: 59 Observed: 60
Chance of precipitation: 0.01 – 0%
Observed: 0.00

Monday (Noon to Midnight):
High: 85 Observed: 87
Chance of precipitation: 0.01 – 0%
Observed: 0.00

Tuesday morning (Midnight to Noon):
Low: 61 Observed: 57
Chance of precipitation: 0.01 – 0%
Observed: 0.00

Tuesday (Noon to Midnight):
High: 85 Observed: 88
Chance of precipitation: 0.01 – 0%
Observed: 0.00

Wednesday morning (Midnight to Noon):
Low: 59 Observed: 60
Chance of precipitation: 0.01 – 10%
Observed: 0.00

Wednesday (Noon to Midnight):
High: 83 Observed: 79
Chance of precipitation: 0.01 – 10%
Observed: 0.00