{ "number": 726, "headline": "September 7, 2025 Sunday Evening Update", "standfirst": "Early fall cold front sweeps through Eastern US + quiet Atlantic tropics", "desk": "tropics", "dateline": { "place": "Weather Trader", "state": null, "lat": null, "lon": null, "site_key": null, "site_name": null, "site_url": null, "accent": null }, "edition": "2025-09-08", "published": "2025-09-08T01:16:32.762000Z", "updated": null, "access": "free", "body_html": "
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Good evening! Hopefully everyone enjoyed the wonderful weekend that shaped up today across much of the Eastern U.S. with clear skies and warm temperatures. A bit cooler tomorrow as Canadian continental air filters all the way into the southeast behind a cold front.

The Atlantic tropics have gone DORMANT again \u2014 and may be quiet especially in the Main Development Region (MDR) for the next 7-10 days, or until a healthy enough tropical wave comes off Africa that can survive the otherwise hostile environmental conditions (dry air, high stability, dust, wind shear).

Sunday Evening Weather Update

  1. Invest 91L is gone \u2014 completely poofed this weekend from 90% chance of development to 0% for one of the most spectacular missed genesis forecasts by humans and machine (models)

  2. Hurricane Kiko has weakened to Category 2 on a WNW course that will take the system to the north of the Hawaiian Islands.

HRRR | Precipitable Water Next 48-hours

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Dry air behind a strong continental cold front will eventually be moistened by return flow across the Plains into the Midwest and Great Lakes + Atlantic / Gulf of Mexico moisture along that stationary boundary.

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Weather | Fronts this Evening

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Some storms in the west across the mountains helping to thin out the ongoing forecast fire smoke coming from Canada. The smoke is reaching Denver and OKC and will add some haze to the evening sky.

Smoke Analysis | 11 PM ET

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Pop Up Storms in the northern Rockies + Florida

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Mid-Level Humidity = very dry behind the Canadian cold front and trough dipping into central Georgia this evening

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North America Upper Level Height Anomaly | AIFS 18z | Next 10-days

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Strong ridging builds across Canada over the next 7-10 days for a much warmer pattern across the Lower 48. Hard to get any Arctic air to flood southward. However, unsettled weather will result from several cut-off troughs that necessarily have to go around the ridge.

ECMWF EPS 12z | 7-day Temperature Anomaly | Week 1 (Sept 7-13)

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ECMWF EPS 12z | 7-day Temperature Anomaly | Week 2 (Sept 14-20)

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RTMA Temperatures and Anomaly | 7:30 PM ET

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Lower 48 is -2.9\u00b0F below normal with cool anomalies of more than 30\u00b0F below normal across central Plains.

HRRR Radar Simulation Next 48-Hours

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Heavy rain along the frontal boundary in Florida + showers in the Great Lakes by Tuesday

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Rainfall Next 48-hours | NWS NDFD

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Low Temperatures Monday

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Well below normal temperatures in the Great Lakes in the 30s \u2014 chilly!

High Temperatures Monday

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Very comfortable across much of the Lower 48 with only 26 million at/above 90\u00b0F

7-Day Precipitation from NOAA WPC

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Atlantic Hurricane Season

2025 Hurricane Season [Day 99]. My FORECAST for this year is 14 named storms, 7 hurricanes, and 3 major hurricanes (near average) BUT that might be generous

2025 Season to Date: 6 named storms, 1 hurricanes, and 1 majors | ACE = 40 ACE of Erin: 32.2 (140-knots maximum wind)

ECMWF 10-Days Integrated Vapor Transport | 12z cycle

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Flagship model simulation for next 10-days \u2014 best chance for \u201csomething\u201d is a wave that emerges next weekend!

VERY quiet \u2014 dormant Atlantic \u2014> ghost town! I think we\u2019ll need to dial back the seasonal forecasts a little bit mainly because we\u2019ll sail through the peak of the season with NOTHING.

ECMWF 18z | Precipitable Water Next 6-days

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A tropical wave by next weekend coming off Africa is the next decent shot at a tropical storm.

Atlantic Basin Outlook | 8 PM ET Update

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Atlantic Satellite Imagery | Water Vapor

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Tropical wave generating convection northeast of Brazil at low latitudes but not being pegged for development.

Infrared and GeoColor Imagery

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NOAA Tropical Surface Analysis | 18z

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Atlantic Tropical Waves = 3 including generating moderate convection.

ECMWF SST and Anomaly | Atlantic

NASA Dust 5-day Forecast

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An early September dust plume helped to wipe out Invest 91L creating a dry and stable environment ahead of the tropical wave \u2014 and another one is on its heels. The dust is the symptom or proxy of the Saharan Air Layers (SAL) coming off Africa at about 20\u00b0N and ruining the chances of tropical storm formation.

ECMWF EPS 18z Ensemble | Active Cyclone Tracks Through 6-days

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Tiny chance of a development (5%)

ECMWF EPS 12z Ensemble | Active Cyclone Tracks Through 10-days

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A handful of members with tropical waves that develop \u2014 at most 20%

ECMWF EPS 12z Ensemble | Active Cyclone Tracks Through 15-days

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Additional members \u201ccatch fire\u201d with tropical waves into major hurricanes \u2014 again in the 20% to 30% range, which is near climatology into third week of September.

AIFS-ENS Comparison at 12Z | Active Tracks at Day 10

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Very excited about this tropical wave \u2014 high chance > 90%

AIFS-ENS Comparison at 12Z | Active Tracks at Day 15

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Plenty of options \u2014 but, as we saw with Invest 91L \u2014 don\u2019t count your chickens before they hatch.

Eastern Pacific Tropical Update| Hurricane Kiko

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Category 2 \u2014 WNW track at 13 mph \u2014 will safely pass north of Hawaii.

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Kiko is a very small tropical cyclone \u2014 previously a Category 4 Hurricane

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Looks beautiful all on its own in the central Pacific!

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Kiko is a massive latent heat engine in the middle of a vast sprawling dry atmosphere over the Pacific Ocean

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HAFS-A and HAFS-B (18z) for Kiko | Analysis \u2014 resilient over colder water (SST 26\u00b0C)

Hurricane Kiko

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The Atlantic tropics have gone DORMANT again \u2014 and may be quiet especially in the Main Development Region (MDR) for the next 7-10 days, or until a healthy enough tropical wave comes off Africa that can survive the otherwise hostile environmental conditions (dry air, high stability, dust, wind shear).

Invest 91L is gone \u2014 completely poofed this weekend from 90% chance of development to 0% for one of the most spectacular missed genesis forecasts by humans and machine (models)

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