A Recipe for Rain, Southwest Style

Much of Texas and the Southern Plains are currently in a worsening drought situation. The latest U.S. Drought Monitor released today shows D3 (Extreme) and D4 (Exceptional) drought from central Texas east northeast into southern Arkansas and the northern three-quarters of Louisiana.

Dryness has been slowly developing since the beginning of  summer, but the drying really accelerated in the past four to six weeks.

This map shows the change in drought status from September 22 to October 20, 2015

While Texas CoCoRaHS observers may not have been seeing much but dust in their rain gauges recently, that is about to change.  A "perfect" combination of circumstances will likely bring drought-busting rain to the region the next several days, but that has a down side as well.

The first weather feature in this recipe is an upper level trough with a closed low situated over the Four Corners. On the east side of this trough strong southwest winds are directing air into central Texas.

The 500 millibar map for 7:00 a.m. CDT October 22, 2015.

The second weather feature is Hurricane Patricia, which reached Category 4 strength this afternoon with sustained winds of 130 mph. Late this afternoon Patricia was located about 250 miles off the coast of Mexico moving northwest at 12 mph. The hurricane will turn north by tomorrow morning and likely make landfall on the Mexican coast late Friday afternoon or evening. Patricia will bring abundant moisture into Mexico, moisture that will be tapped by the trough over the southwest. Hurricane Patricia is the ninth Category 4 or 5 hurricane in the eastern Pacific this year, a new record. The latest updates on Patricia can be found at the National Hurricane Center web site.

Water vapor image of Hurricane Patricia at 1:45 p.m. PDT October 22. The eye of the storm is only 12 miles in diameter.

The third ingredient to this recipe for rain is moist flow off the Gulf of Mexico.

The 850 millibar map (~5000 feet) showing winds and relative humidity for 7:00 a.m. CDT Saturday, October 24.
Light green is RH of  =>70%, dark green is =>90%

All of this is expected to come together over Texas this weekend. The National Weather Service Office in San Antonio/Austin created a nice graphic showing how all of this is expected to come together.

This graphic shows the setup for the expected rain this weekend over Texas.

Rain is most welcome, but too much rain is not. The Quantitative Precipitation Forecast (QPF) for the three-day period ending Sunday evening at 7:00 CDT shows that much of the southeastern half of Texas will get several inches of rain, with a potential for as much as 13 inches between Austin and Dallas/Ft. Worth.

Quantitative Precipitation Forecast for the 72-hour period ending Sunday, October 26 at 7:00 p.m.

Of course this forecast may change based on how the weather features finally come together, but the primary message here is there will be lots of rain in a relatively short period, primarily from now through Saturday night. That means flooding. Just six months ago drought-ending rain occurred in Texas and Oklahoma, but it also resulted in major and in some cases record flooding on many rivers in Texas. This weekend's rain will not necessarily be a repeat of last May, providing there aren't successive heavy rain events in the next month or so. By early next week the focus of heavy rain will be southern Louisiana as the system moves east

A wide swath of central Texas and south-central Oklahoma is under a flash flood watch beginning Friday morning into Sunday. Be sure to visit your local National Weather Service web site for the latest information and updates.

Watches, warnings, and advisories in effect as of 5:08 p.m. CDT

Cyclones Aplenty

If you're a tropical weather enthusiast the last week to ten days has been an interesting period. In the Atlantic Danny was briefly a hurricane, but fizzled out pretty quickly and fell apart last Monday in the eastern Caribbean producing heavy rain but not much else. In the wings was Tropical Storm Erika, which in the early stages appeared to be a threat to Florida. However, Erika never did make hurricane strength. It quickly fell apart as strong wind shear and the mountains of Hispaniola combined to weaken it, and the storm dissipated off the northeast coat of Cuba. Erika did bring heavy rain to the Caribbean last week and the remnant trough of low pressure continued to produce heavy rain across Florida and the southeast coast this weekend.

7-day accumulated rainfall for Puerto Rico ending the morning of 8/31/2015

24-hour precipitation for the southeastern U.S. ending the morning of 8/31/2015

A low pressure system that move off the west coast of Africa became Tropical Storm Fred Sunday,  Hurricane Fred early this morning, and was downgraded to Tropical Storm this evening. Fred is a small cyclone and likely will be moving into unfavorable upper air conditions in the next few days. Current forecasts call for it to be only a tropical depression by the end of the week.

Forecast track for Fred.

Conditions are even more interesting in the central Pacific, where three hurricanes are spinning.

NOAA GOES-West image of three hurricanes in the Pacific: Kilo (left), Ignacio (middle), and Jimena (right).

Hurricane Kilo is a Category 4 hurricane located several hundred miles east of Wake Island. Hurricane Ignacio is a Category 2 storm (it was a Category 4 storm on Sunday) located about 350 miles east of Honolulu. Hurricane Jimena is another Category 4 storm with peak sustained winds of 145 mph. Ignacio is not expected to directly threaten Hawaii, but it is producing dangerous surf conditions. This is the first time three major hurricanes (category 3 or higher) have been observed over the central Pacific at the same time.

The eye of Hurricane Jimena taken by astronaut Kimiya Yui on the International Space Station

The tropical cyclone activity in the Pacific is being supported by some very warm water. Below is an image of the Pacific sea surface temperature anomaly as of today.

Sea surface temperature anomaly on August 31. The water over which the hurricanes are located is 1.5°C to more than 2.5°C (2.7°F to 4.5°F) above normal.

Finally Tropical Depression 14-E developed in the eastern Pacific and late today was located about 700 miles south of the southern tip of Baja California. It is expected to strengthen to a tropical storm in the next 24 hours and turn to the north.