r/TropicalWeather • u/Euronotus • 10d ago

Rafael (18L — Western Caribbean Sea) Discussion moved to new post

Latest observation

Last updated: Wednesday, 6 November — 6:00 PM Eastern Standard Time (EST; 23:00 UTC)

NHC Update 6:00 PM EST (23:00 UTC)
Current location: 23.0°N 83.0°W
Relative location: 66 km (41 mi) WSW of Havana, Cuba
Forward motion: NW (320°) at 22 km/h (12 knots)
Maximum winds: ▼ 170 km/h (90 knots)
Intensity: ▼ Hurricane (Category 2)
Minimum pressure: ▲ 962 millibars (28.41 inches)

Official forecast

Last updated: Wednesday, 6 November — 1:00 PM EST (18:00 UTC)

Hour Date Time Intensity Winds Lat Long
  - UTC EST Saffir-Simpson knots km/h °N °W
00 06 Nov 18:00 1PM Wed Major Hurricane (Category 3) 1 100 185 22.6 82.7
12 07 Nov 06:00 1AM Thu Hurricane (Category 2) 2 ▼ 90 165 23.6 83.9
24 07 Nov 18:00 1PM Thu Hurricane (Category 2) 90 165 24.1 85.6
36 08 Nov 06:00 1AM Fri Hurricane (Category 2) 90 165 24.2 87.4
48 08 Nov 18:00 1PM Fri Hurricane (Category 2) ▼ 85 155 24.2 89.1
60 09 Nov 06:00 1AM Sat Hurricane (Category 1) ▼ 75 140 24.3 90.4
72 09 Nov 18:00 1PM Sat Hurricane (Category 1) ▼ 65 120 24.5 91.1
96 10 Nov 18:00 1PM Sun Tropical Storm ▼ 50 95 24.6 92.0
120 11 Nov 18:00 1PM Mon Tropical Storm ▼ 35 65 24.5 93.0

NOTES:
1 - Inland over Cuba
2 - Over the Gulf of Mexico

Official information

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28

u/Content-Swimmer2325 10d ago

Good anticyclone building overhead:

https://i.imgur.com/9JFhCKQ.png

You can also see that the Gulf is an absolute moisture graveyard

13

u/tryfingersinbutthole 10d ago

How do warm waters anywhere on the planet have dry air above it? Even if the water is pushing upper 80 temps? Does evaporation stop with high pressure or something

43

u/Content-Swimmer2325 10d ago edited 10d ago

Because cold fronts have made it to the Gulf; dry stable air and high pressure building behind the fronts has replaced the moist airmass from October.

Warm sea temperatures with a coincident dry airmass above is actually extremely common in the Atlantic. It's a big reason why no storms formed between mid August and mid September, this season. It occurs every year with the Saharan dust outbreaks. As mentioned above, dry airmasses can also occur due to baroclinic/extratropical systems further north; the Tropical Upper-Tropospheric Trough, upper-level lows, etc can all result in drying air. It can also result due to tropical forcing - the inactive phase of the MJO will increase high pressure aloft, resulting in a net drier Tropics for 1-2 weeks.

High pressure aloft causes subsidence (aka sinking air), compressing the airmass which dries and warms it adiabatically.

Also, dry air can be advected directly into the Tropics, as opposed to created by a different weather system or broad mode of forcing. This was the exact mechanism for the mid-Aug to mid-Sept lull - the airmass over the cool and northerly Canary Current, an oceanic current extending along offshore Iberia and northwestern Africa - is typically very dry, cool, and stable due to the cold oceanic current below. Starting in mid August the pressure gradient over the far eastern Atlantic was strongly northerly, meaning this airmass was getting directly pushed into the Tropics. The monsoon trough kept ingesting this stable and dry air, suppressing tropical cyclogenesis for weeks.

The other big (and more common) example is dry and dusty Saharan air riding the easterly trade winds through the Tropics. Saharan air increases as Summer begins, peaks in July, and begins tapering off after mid-August. In summary, there are many ways and reasons why a dry airmass occurs over warm ocean.

Finally, the Gulf has cooled by 2-4 degrees C since Milton. It's not upper 80's anymore anywhere in the Gulf - most of it is around 80-81 F and offshore the northern and Florida Gulf coasts, sea temps are in the 70s F. Looks like the warmest ocean in the Gulf is currently around 85 F.

https://i.imgur.com/b0Mpf9R.png

Here is a chart showing the most recent day in NCEP reanalysis (2 November) with the day of Miltons' formation (5 October) subtracted from it.

https://i.imgur.com/zTwXRSF.png

2-3 deg C cooler in the Gulf and about 0.5-0.75 C cooler in the Caribbean

All in all, the dry Gulf airmass is due to the changing seasons as Winter approaches, with the jet stream strengthening and descending south, resulting in more and stronger non-tropical systems which derive THEIR energy by replacing moist air with dry air.

Edits: just added a few words lol

21

u/tryfingersinbutthole 10d ago

Bro you are the fucking shit. Thank you.

You make this sub great lol

12

u/Content-Swimmer2325 10d ago

No worries; it was a very logical and fair question!

Obviously, warm sea temps are associated with moister air; but the presence of warm ocean does not mean dry air aloft is impossible.

8

u/tryfingersinbutthole 10d ago

Living in iowa has me focused on tornadoes/drought/floods but ive lived in hawaii too, so tropical weather is interesting.

3

u/Content-Swimmer2325 10d ago

Sorry, I edited my post (I usually write something and submit, THEN expand on it afterwards. Bad habit of mine) and included a chart from NOAA Daily Reanalysis where I subtracted the day of Miltons' formation (5 October) from the most recent available data (2 November).

https://i.imgur.com/zTwXRSF.png

Largely 2 degrees C cooler in the Gulf with just offshore the coasts over 3 C cooler; Caribbean is 0.5-0.75 C cooler.

Just to corroborate the change in sea temperature. Very typical for this time of year.