Newton Sweeps into U.S. with Strong Wind, Heavy Rain, Deep Moisture

Former Hurricane Newton swept from Mexico’s Gulf of California into southeast Arizona between 1 and 2 pm MDT Wednesday afternoon. Analyzed as a 45-mph tropical storm at noon MDT Wednesday, the fast-weakening Newton was classified as a remnant low by NHC a couple of hours after its international border crossing. In its final discussion on the system, NHC said: “Based on the data available to us at this time, we do not think that Newton moved into southern Arizona as a tropical cyclone.” Only a handful of systems have been officially designated as tropical storms while in Arizona, including Hurricane Katrina (1967), Hurricane Lester (1992), and Hurricane Raymond (1989). In 1997, Hurricane Nora tracked up the Colorado River valley along the Arizona/California border as a tropical storm.


Figure 1. Natural-color satellite image of Newton over southeast Arizona at 2035Z (4:35 pm EDT) Wednesday, September 7, 2015, about an hour after it crossed into the state. Image credit: CSU/RAMMB/CIRA.

Newton still brought a dose of strong wind and torrential rain to the state. About 40 miles south of Tucson, a remote automated weather station located at 7120 feet near the top of Mt. Hopkins recorded several hours of high wind from the east while Newton was still a tropical storm in Mexico. The winds peaked at 9:19 am MDT with a report of 52 mph gusting to 66 mph. Other high-altitude stations also reported strong gusts, including 58 mph at Miracle Valley (elevation 7677 feet). Rainfall totals of 3” - 5” were scattered along the track of Newton at higher elevations across southeast Arizona and southwest New Mexico, with 1” - 2” common at lower elevations. A PWS on the summit of Mt. Graham reported more than 4”.

Newton’s presence lives on in the form of deep tropical moisture funneled well ahead of the storm into the Central Plains and Midwest across a preexisting frontal system. At Lincoln, IL, the atmospheric sounding taken at 12Z (8:00 am EDT) Thursday showed 2.54” of total precipitable water (TPW)--the amount of water vapor in a column of air from the surface upward. This is the second-highest TPW recorded on any date since regular balloon-borne soundings began in the Lincoln/Peoria area in 1949, topped only by 2.66” on July 8, 1949. Showers and thunderstorms dropped 3” - 5” rains on Wednesday afternoon and evening across parts of southeast Kansas, eastern Iowa, and western Michigan (see Figure 2). The NWS Weather Prediction Center is calling for a slight risk of rainfall exceeding flash flood thresholds on Thursday and Friday across parts of Kansas, Missouri, Illinois, and Indiana.


Figure 2. Multisensor analysis of total rainfall (in inches) from 12Z (8:00 am EDT) Wednesday, September 7, to 12Z Thursday, September 8. Image credit: NOAA/NWS Advanced Hydrologic Prediction Service.

Tropical wave 93L near the Lesser Antilles little threat to develop
An area of low pressure located about 300 miles east of the northern Lesser Antilles Islands late Thursday morning was  headed west-northwest at about 15 mph. This system was designated Invest 93L by NHC on Thursday morning. Satellite images show that 93L has developed plenty of spin but only a small amount of heavy thunderstorm activity. Spinning clouds in mid to upper levels of the storm briefly created the false appearance that 93L had an eye Thursday morning, but the system has had no signs of a surface circulation center thus far. The disturbance was battling plenty of dry air, as seen on water vapor satellite loops, and the 8 am EDT Thursday run of the SHIPS model showed the humidity at mid-levels of the atmosphere was about 45 - 50%, which is normally too dry to support tropical storm formation unless wind shear is very low. Wind shear was a moderate 10 - 20 knots over 93L, and sea surface temperatures (SSTs) were a  warm 29°C (84°F.)


Figure 3. Latest satellite image of 93L.

Forecast for 93L
There is very little model support for the development of 93L, with none of the 00Z Thursday operational versions of our three reliable models for predicting tropical cyclone genesis--the GFS, UKMET and European models--predicting development. Only 4% of the 50 ensemble members of the European model predicted development, and none of the 20 members of the GFS model ensemble did so. The 8 am EDT Thursday run of the SHIPS model predicted that wind shear would remain moderate, 10 - 20 knots, over the next five days, but the atmosphere would remain very dry, which should make any development slow to occur. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave this system 2-day and 5-day development odds of 10% and 20%, respectively. Invest 93L will continue moving west-northwest to northwest at about 15 mph over the next five days, which should put it a few hundred miles southeast of the coast of South Carolina by Tuesday.

African tropical wave may develop early next week
A tropical wave that emerged from the coast of Africa on Tuesday was bringing a modest area of disorganized heavy thunderstorms to the waters of the tropical Atlantic about 500 miles southwest of the Cabo Verde Islands on Thursday morning, as seen on Meteosat satellite images. This tropical wave could develop into a tropical depression by early next week, predicted our top three models for hurricane genesis, the UKMET, GFS and European models, in their 0Z Thursday runs. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave this system 2-day and 5-day development odds of 10% and 60%, respectively. The long-range models are showing a west-northwesterly track for this storm into the Central Atlantic to a location where few storms ever become a threat to the Lesser Antilles Islands or North America.

Bob Henson and Jeff Masters