James Peacock

The latest NHC forecast is shifted a little south of the previous one.

With this, the potential maximum strength of Melissa increases, but the risk of eyewall impacts on Jamaica reduces albeit only slightly.

Sadly, the extreme rainfall risk there remains very high.

A big implication of this is that unsettled weather can lead to flooding more quickly in a warmer climate.

If we (somehow!) had a sequence of unsettled weather now that was identical to one fifty years ago, we'd observe more rainfall, hence higher flood risk, this time around.

This temperature to moisture capacity relationship is one reason why in a warming climate, there are parts of the world - including NW Europe - predicted to see an increased typical magnitude of both droughts & floods.

Another one is hotter spring-summer weather (faster drying-out).

The in places very high rainfall totals are tied to those low pressure systems drawing across much warmer than usual air for the time of year.

Every 1°C warmer the air is, it can hold ~7% more water vapour. Active weather fronts fulfil that potential (air saturates => rainfall).

Areas of low pressure look set to dominate the weather over western Europe for the next week or so.

Until ~next Friday, associated wet weather focuses on Portugal & into Spain, before spreading further northwest.

Parts of Portugal could see 100-150 mm in the next ten days.

Here we see a rare instance of the automated summary on the NHC active tropical cyclones page showing "Moving: at mph" due to Melissa being pretty much stationary.

It's just standing there, menacingly.

Of course, there are also runs that take Melissa further northeast to the point that land interaction keeps it from becoming more than a low-end hurricane.

Alas, those still bring copious amounts of rain to Jamaica & in many cases southern Haiti too.

In the ECMWF ensemble there are even some runs that have Melissa brushing central America as a major hurricane.

This concerns me even more because having the spread reach that far southwest makes the not quite as far southwest, high-end hurricane scenarios more plausible.

I really don't like that the latest forecast runs include some that track Melissa due west or even south of west in the near future.

That's the scenario that would open the door to it becoming a high-end hurricane with peak sustained winds somewhere above 155 mph.

When it comes to cumulative impact from a tropical cyclone, forecasts don't get much more ominous than than this one is for Jamaica.

Potential for prolonged damaging winds & heavy rainfall from Melissa, which is forecast to become a category 4 hurricane if it stays over water.

QBOi‐SNAP‐QUOCA workshop: improved simulations of the stratosphere for better predictions of weather, climate and extreme events Click on the article title to read more.

QBOi-SNAP-QUOCA workshop: improved simulations of the stratosphere for better predictions of weather, climate and extreme events

Meeting report from the @wcrpclimate.bsky.social APARC workshop in Cambridge earlier this year

Free to view in @rmets.org Weather: doi.org/10.1002/wea....

Wild that we still have GFS/AVNI initialising Melissa with too much vertical depth, resulting in a track toward Haiti when all other models head further west, & many of them by a large margin. The NHC favour the more western scenarios.

Imagine if all we had to assess was GFS 😨

If #Melissa finds its way south-southwest of Jamaica in several days, this environment has the highest ceiling for any Atlantic tropical cyclone I can remember.

Big, strong, slow-moving hurricanes like what #Melissa may become are when things like Oceanic Heat Content will start to matter a lot.

Autumn doing autumn things 🍂 🍄‍🟫

The wind speed graph view features some astonishingly strong scenarios, but also plenty of weaker ones, emphasising the uncertainty.

Believe it or not, I didn't even choose the most extreme scenario among the 00z hurricane model runs.

In short, keep a close eye on Melissa's movement in the next few days.

I'm not saying this would definitely happen, but if Melissa follows the low-level westward steering for the next few days instead of heading more northward, then with huge oceanic heat content & a favourable atmosphere above, there's legit potential for a high-end hurricane.

So this serves as a good reminder that the warnings are for the possibility, not guarantee, of severe weather.

If you might be negatively affected, it's worth being prepared all the same.

Considering the short lead time, there's disturbingly little consistency between forecast model predictions for the rainfall tonight through tomorrow.

The Met Office's rainfall warning covers for all scenarios. Odds are not all areas within the warning zone will see much rain.

The overnight ECMWF det. run took that signal & ran with it for the first week of November, even escalating it further, but for 5th-6th November it was among the warmest runs relative to its ensemble counterpart, so best viewed with scepticism.

A notable signal for unseasonable warmth in much of Europe continues for around the turn of the month.

Tied to a broad Atlantic low, Europe high pattern. Usual uncertainty on details but e.g. England could well see some days reaching 16-18°C quite widely, albeit the feel tempered by wind.

The initial forecast for Melissa is as interesting as I expected. Model guidance varies widely, some runs starting to move it toward the Bahamas by Thu, while others track it slowly toward the western Caribbean instead.

The NHC have played it safe with a weighted blend.

As anticipated, the 2025 Atlantic hurricane season's 13th named storm is now confirmed for a 15:00 UTC designation.

This is almost a month sooner than the median date of the 1981-2020 seasons that reached 13.

Melissa's initial forecast is going to be... interesting.

With invest 98L reportedly & visibly developing a well defined low level circulation, with observed wind speeds as high as 45 mph, I'll be surprised if 15:00 UTC doesn't bring the official designation of tropical storm Melissa by the NHC.

A potentially high-impact system 👀

The Netherlands' impressive flood defence system will be put to the test this weekend as a deep low moves slowly toward the Baltic Sea or thereabouts.

Strong winds are predicted to race straight down the North Sea, building a storm surge. Just how big remains to be resolved.

Rainfall-wise, it appears southern England is in for its 3rd soaking in the space of 5 days, with over a 1 in 3 chance of at least 20 mm.

If so, the 5-day totals from last Sunday could widely be in the 60-80 mm range. Quite a turnaround after a fortnight with near-zero rainfall.

The ECMWF ensemble gives a high probability of wind gusts exceeding the 99th percentile widely in mainland north-western Europe.

That equates to wind gusts in the ~40-50 mph range.

However, probability for gusts to ~55 mph or higher is mainly low away from windward coasts.

Monitoring the potential for a powerful windstorm to affect parts of north-western & central Europe this Thu-Fri.

Guidance has begun to favour a path that brings strongest winds to the Low Countries while heaviest rain affects S(E) UK, Belgium, & Netherlands, perhaps NW Germany.

Large variation of temperatures in NW Europe has been a feature of many recent forecast model runs for the rest of this month & into November.

The overnight GFS is among the most extreme, with e.g. England barely managing double digits this Sunday, yet reaching 17-20°C to begin November.

Indeed 😄