{ "number": 732, "headline": "September 12, 2025 Friday Evening Update", "standfirst": "NHC up to orange 40% for Eastern MDR tropical wave", "desk": "tropics", "dateline": { "place": "Weather Trader", "state": null, "lat": null, "lon": null, "site_key": null, "site_name": null, "site_url": null, "accent": null }, "edition": "2025-09-12", "published": "2025-09-12T23:49:00.431000Z", "updated": null, "access": "free", "body_html": "
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Good Evening! This has been a very difficult week for the country and I\u2019m hopeful everyone can take some time outside this weekend to enjoy nature and the weather. I\u2019ll try to keep the hurricanes away as long as possible, but my antenna are up for the next few tropical waves in the MDR pipeline.

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Lower 48 Precipitable Water Forecast | Next 5-days

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Tropical Storm Marco enters the frame in a few days and should become a hurricane prior to moving over cooler waters off Baja California Sur.

A cut-off low spins of the Southeast into next week on the \u201cwave breaking\u201d side of the strong blocking ridge centered in Canada pulling up as much moisture as it can through the U.S. Plains. The southerly flow is HOT \u2014 well above normal pushing 100\u00b0F.

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Weather | Fronts this Evening

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RTMA Temperatures and Anomaly | 6:30 PM ET

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90s across the central U.S. including St. Louis

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Lower 48 is above normal +3.7\u00b0F

Low Temperatures Saturday Morning

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Even in the hottest daytime regions of the central Plains, still cools down nicely.

High Temperatures on Saturday

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Well into the 90s and pushing 100\u00b0F maybe in Iowa. 79 million at least 90\u00b0F

High Temperatures on Sunday

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Heat moves eastward a smidge \u2014 very hot across the Plains into mid-Mississippi River Valley \u2026 77 million at least 90\u00b0F

Rainfall Next 72-hours | NWS NDFD

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Weather | Fronts on Saturday

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7-Day Precipitation from NOAA WPC

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North America Upper Level Height Anomaly | AIFS 12z | Next 10-days

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Canadian blocking ridge breaks down toward Days 8-10 with more \u201cpolar vortex\u201d influence from the Arctic and some action from the Pacific.

Troughs and cut-offs dominate the Lower 48 under the ridge until then.

ECMWF EPS 12z | 7-day Temperature Anomaly | Week 1 (Sept 12-18)

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ECMWF EPS 12z | 7-day Temperature Anomaly | Week 2 (Sept 19-25)

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Atlantic Hurricane Season

2025 Hurricane Season [Day 104]. My FORECAST for this year is (still) 14 named storms, 7 hurricanes, and 3 major hurricanes (near average)

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

ECMWF 12-Days Integrated Vapor Transport | 12z cycle

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A parade of tropical waves \u2014 I can count 4 but at least here in the ECMWF 12z flagship model, none \u201ccatch fire\u201d \u2026 but these are all candidates.

Germany ICON 18z | Precipitable Water Next 6-days

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ICON model + GFS are more aggressive with 2 tropical waves \u2026 I just can\u2019t believe we\u2019ll get nothing out of this sequence \u2014 so if we split the baby, then 2 named storms in the next 8-12 days (Gabrielle and Humberto).

NOAA GFS 18z | Vorticity 12-day Forecast

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Happy Hour GFS 18z delivers a museum quality forecast model with 4 storms/hurricanes all in a row. Of course, we usually don\u2019t put much stock in 18z models because there are no upper-air soundings (balloons) \u2026 but this is a shift/flip from what GFS was doing earlier today.

Atlantic Basin Outlook | 2 PM ET Update

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40% chance of development for a tropical wave in the far Eastern Atlantic \u2026 that is generating very little convection. Already poofed?

Atlantic Satellite Imagery | Infrared

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Very little convection across the MDR \u2014 stable and dry, but that will trend in the other direction.

Water Vapor | Mid-level

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SST and SST Anomaly | ECMWF 12z analysis

NOAA Tropical Surface Analysis | 12z

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Atlantic Tropical Waves = 4 with our 40% NHC

Eastern Atlantic and Africa Infrared Satellite

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The next tropical wave over Africa \u2014 as we\u2019ve seen all season \u2014 is convectively active and looks great \u2014 until it hits the Atlantic and goes poof. I think this next one will be different \u2014 further south.

ECMWF EPS 12z Ensemble | Active Cyclone Tracks Through 5-days

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This is not a strong signal for the 2 waves to be TD/TS but perhaps a weak surface circulation will hold together on the long westward trek to more favorable environment near the Lesser Antilles and into Western Atlantic.

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

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Again we see some members with hurricanes creeping out of the Caribbean into the Gulf \u2014 this sneaky ensembles are hopefully not indicative of something nefarious.

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

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This is a STRONG signal for a hurricane or two \u201csomewhere\u201d and there are many very concerning situations \u2014 but past our forecast horizon (September 27th)

AIFS-ENS Comparison at 12Z | Active Tracks at Day 6

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AIFS ENS remains very excited about this tropical wave \u2014 high chance > 90%

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

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

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A more active Atlantic basin for sure, but thankfully everything looks to be recurving or staying away off the U.S. mainland.

Eastern Pacific Tropical Update | Tropical Storm Marco

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NHC is just under hurricane strength with Marco (13E) but I\u2019m pulling for it to reach H status \u2014 and HAFS in 2-3 days brings it up to Category 1 moving away from Mexico eventually over cold water.

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Tropical Storm Marco enters the frame in a few days and should become a hurricane prior to moving over cooler waters off Baja California Sur.

A cut-off low spins of the Southeast into next week on the \u201cwave breaking\u201d side of the strong blocking ridge centered in Canada pulling up as much moisture as it can through the U.S. Plains. The southerly flow is HOT \u2014 well above normal pushing 100\u00b0F.

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