| Above: Tropical Storm Karen at 12:05 pm EDT September 22, 2019. At the time, Karen had top winds of 40 mph. Image credit: NOAA/RAMMB. |
Tropical Storm Karen formed on Sunday morning just east of the Windward Islands. Karen was bringing heavy rains to the coast of South America and the Windward Islands, particularly Trinidad and Tobago, at midday Sunday. Karen’s formation gives the Atlantic 11 named storms, 4 hurricanes, 2 intense hurricanes, and an ACE index of 80 so far in 2019. An average season typically has 8 named storms, 4 hurricanes, 2 intense hurricanes, and an ACE index of 72 by September 22.
 |
Figure 1. Radar image of Tropical Storm Karen from the Barbados radar at 11 am EDT Sunday, September 22, 2019. Karen was bringing heavy rains to the coast of South American and the Windward Islands, particularly Trinidad and Tobago. |
The Barbados airport recorded sustained 10-minute average winds of 38 mph, gusting to 49 mph, at 6 am local time Sunday. Wind gusts up to 44 mph were observed on St. Lucia on Sunday morning. Karen’s rainfall in Trinidad and Tobago triggered flooding on Sunday morning (see tweet below). A personal weather station in Trinidad recorded 3.82” of rain as of 1 pm EDT Sunday.
Newly formed Tropical Storm #Karen is producing serious flooding right now in Trinidad and Tobago . https://t.co/EbZamIF20E
— Katie Walls (@KatieWallsWSB) September 22, 2019
Satellite images early Sunday afternoon showed Karen’s well-defined surface circulation was exposed to view, with the system’s heaviest thunderstorms located to the south. The lack of thunderstorms on the north side was due to dry air there; this dry air was being brought into the core of the disturbance by strong upper-level winds out of the northeast, associated with the upper-level outflow from Tropical Storm Jerry. These winds were creating high wind shear of about 20 knots. However, SSTs were warm, near 29.5°C (85°F), and the atmosphere along the south side of Karen was moist.
Forecast for Karen
Wind shear over Karen is predicted to increase to a very high 25 – 30 knots on Monday. This will likely keep any development slow, and may be enough to destroy the storm. Karen will turn to the northwest on Monday, following a weakness in the ridge of high pressure to its north, with the model consensus showing a track through the Virgin Islands, just east of Puerto Rico, on Tuesday. Heavy rains will be the main threat from Karen to the islands.
Once Karen reaches the waters north of Puerto Rico on Wednesday, the wind shear affecting it is predicted to abate, which should allow strengthening. The predominant model consensus shows a ridge of high pressure building north of Karen late in the week, forcing the storm to track to the west towards The Bahamas. In this scenario, the mainland U.S. could be at risk in about a week to 10 days—though the uncertainty in this outcome is high.
 |
| Figure 2. Tropical Storm Jerry at 12:05 pm EDT September 22, 2019. At the time, Jerry had top winds of 65 mph. Image credit: NOAA/RAMMB. |
Tropical Storm Jerry headed towards Bermuda
After grazing the Leeward islands on Saturday morning, Jerry was located 470 miles south-southwest of Bermuda at 11 am Sunday morning, headed north-northwest at 10 mph. Satellite loops early Sunday afternoon showed that Jerry was struggling with high wind shear, which had distorted the symmetry of the tropical storm and partially exposed the low-level circulation center to view.
A turn to the north and then northeast towards Bermuda is predicted to occur Monday through Tuesday. On this track, Jerry is likely to pass less than 150 miles to the west of Bermuda on Tuesday afternoon through Wednesday morning. During that period, tropical storm-force winds are predicted to extend out 160 – 200 miles to the northeast of Jerry’s center, making it likely that Bermuda will experience tropical storm-force winds. The 11 am EDT Sunday wind probability forecast from NHC gives Bermuda a 57% chance of experiencing tropical storm-force winds. Jerry will also bring heavy rains to Bermuda beginning on Tuesday morning.
With wind shear expected to be moderate to high over the next five days, ranging from 15 to 35 knots, Jerry is not expected to re-intensify beyond Category 1 hurricane status.
 |
| Figure 3. Invest 90L off the coast of Africa as seen by MODIS on Sunday morning, September 22, 2019. Image credit: NASA. |
New African tropical wave 90L likely to develop by Monday
A tropical wave that emerged from the coast of Africa late Saturday was designated 90L by NHC on Saturday night. Satellite images early Sunday afternoon showed that this wave had an impressive circulation with plenty of heavy thunderstorms that were quickly growing more organized. 90L has high model support for development, with the 0Z Sunday operational runs of our three most reliable models for predicting tropical cyclone genesis—the GFS, UKMET, and European—all predicting development by Monday. This system is expected to move west then west-northwest at 15 – 20 mph this week. The latest model runs predict that 90L will most likely be a “fish” storm that will not affect any land areas—except for the southern Cabo Verde Islands on Monday. In their 8 am EDT Sunday Tropical Weather Outlook, NHC gave 90L 2-day and 5-day odds of development of 90%. The next name on the Atlantic list of storms is Lorenzo.
Lorena’s remnants to bring heavy rain to Arizona on Monday
In the Eastern Pacific, Tropical Storm Lorena made landfall in Northwest Mexico along the Gulf of California coast on Sunday morning, then quickly dissipated over Mexico’s high terrain. Lorena’s remnants are expected to bring 3 – 6” of rain along its path through Mexico, and 1 – 2” across much of southern Arizona. The NOAA/NWS Storm Prediction Center has taken the unusual step of putting central Arizona, including the Phoenix area, into a Day 2 outlook for a slight chance of severe weather on Monday, noting that “severe storms, including damaging wind gusts and hail, will develop in the afternoon.” This is only the third time this decade that SPC has placed southern Arizona in a Day 2 slight risk area.
An upper low will be cutting off from the midlatitude jet stream over the Southwest U.S. early next week, which could prolong the chance of showers and thunderstorms across Arizona well into the coming week. Moisture from fast-weakening Tropical Depression Mario, now approaching Baja California, may also get swept into the state around midweek.
Bob Henson contributed to this post.
