July 17, 2023 Outlook: Don doing loops, while Pacific TS Calvin should impact Hawaii

One-sentence summary

Subtropical Storm Don was downgraded to a depression yesterday and remains no threat to land, while ex-Hurricane Calvin in the Pacific is tracking toward Hawaii as a tropical storm with some impacts likely.

Happening now: Calvin hobbles toward Hawaii and Don wandering aimlessly

Of most immediate interest, we turn to the Pacific, where former Hurricane Calvin weakened to a tropical storm on Sunday. Calvin is on a course that will bring it fairly close to the Big Island of Hawaii this week, meaning tropical storm conditions are possible there, assuming it can hold on that long. Even if Calvin does weaken, it is likely to bring rough surf and heavy rainfall.

You can see Hawaii on the left side of this satellite image, as Calvin swirls to the east, heading that way. (Weathernerds.org)

Looking at Calvin on satellite, this is not a particularly strong storm. Maximum winds are 50 mph and continued weakening is expected through tomorrow before it gets to Hawaii. It does have a fair bit of moisture with it, especially on the north and east side which is why portions of Hawaii may be impacted.

Tropical Storm Calvin is expected to graze the Big Island of Hawaii, perhaps as a tropical storm late tomorrow. Rough surf and heavy rain are the main threats. (NHC)

Calvin is currently expected to pass just south of the Big Island, though it remains in the cone. Regardless of the specific track, the impacts should be fairly similar. Rough surf is a given, but also some heavy rain is possible.

Anywhere from 3 to 7 inches of rainfall is possible on the eastern half of the Big Island, with somewhat lesser rains in the other islands.

Current forecasts through Wednesday afternoon in Hawaii show anywhere from 3 to 7 inches on the eastern half of the Big Island, with lesser totals on the other islands. Expect Flood and Tropical Storm Watches to go up later today.

Meanwhile, on the Atlantic side of the coin, there is Don, which is just an adorable system.

Subtropical Depression Don is elongated and has most of its thunderstorms well east of the center. It’s certainly a broad system, coherent but poorly organized. (Tropical Tidbits)

Don is a subtropical depression, and you can see why from the satellite loop above, with general disorganization to its thunderstorms (a lack of bright colors near the swirling center). Speaking of loops, Don intends to do one in the coming days.

Subtropical Depression Don is expected to turn south, slow down, then eventually come back northwest, possibly becoming a subtropical storm again. It remains no threat to land. (NHC)

Don should almost do a complete circle when all is said and done, before it takes off out to sea. There is some chance that Don may reform into a subtropical storm later this week, but we’ll see.

The medium range (days 6 to 10): Atlantic wave watch

There continues to be some support for a potential Atlantic tropical wave heading into the medium range. We briefly mentioned this on Friday with respect to the wave emerging off Africa then. That has since faltered. I would assume this one will as well but there is some model support for something to perhaps come of this in 6 or 7 days.

Another robust tropical wave is emerging off the coast of Africa today, and while it is not expected to develop, it is probably worth watching. (Weathernerds.org)

But to be sure, there are some beefy looking waves coming off Africa right now. If that remains the case in 3 to 4 weeks, it may become more likely that we see something come of them. For now, I would not expect additional development through day 10 of the forecast but I would not rule it out entirely.

Fantasyland (beyond day 10): A little noisier

The extended reaches of the forecast push us into August now, closer to the ramp up in typical hurricane season activity. The GFS model has at times taken that wave we discussed in the medium range section and brought it toward the U.S. or Caribbean islands as a coherent storm in the day 10+ period. But it remains sort of on its own, so we will ignore it specifically for now. Outside of that, there is nothing in particular to pin down.

We had no storms in August of 2022, but based on what we see happening in the atmosphere to kick off August, we would not expect a repeat of that quiet in 2023. Nothing specific to hone in on yet, but we’ll keep you posted.

July 14, 2023 Outlook: We have Don, which should remain averse to land

One-sentence summary

Subtropical Storm Don formed overnight, the 4th named and 5th overall storm of the 2023 season, but it is thankfully no threat to any land.

Happening now: Don!

Invest 94L was upgraded to Subtropical Storm Don early this morning. The “subtropical” designation is technicality. Storms that are tropical in nature form within and feed off of warm, tropical water and air. Being subtropical doesn’t make it any less of a storm, but the process by which it forms and strengthens is more hybrid in nature…like a nor’easter or a tropical storm mashed together. Usually, subtropical storms are a bit lopsided and larger in size. Over time, a subtropical storm can transition to fully tropical, but it’s not clear if Don will do that or if it will even stick around long enough to have a chance.

The forecast track for Don brings it due north, then east, then southeast as it is pushed around by steering currents. (NHC)

As noted yesterday, Don’s forecast track resembles a horseshoe, going north, then east, then southeast. This is because it will be pushed around by various moving parts in the atmosphere over the open ocean.

STS Don is meandering over the open ocean and not expected to have much, if any impact on any land masses, including the Azores (the little islands on the right side of the map). (Weathernerds.org)

Don has 50 mph winds this morning. It’s a respectable looking system, but clearly not terribly menacing looking. The wind field is fairly large, with tropical storm force winds extending out over 200 miles east of the center. Don’s future intensity will be influenced in part by cooler waters, so we should see a slow weakening. It may or may not survive through the weekend, but if it does, it has some chance to get some of its bluster back as it moves south next week, back over warmer water. Eventually it should be picked up and sent away, however.

The medium range (days 6 to 10): Wave emerging off Africa may have a low chance to organize

Some models are picking up on a tropical wave in the Atlantic, which appears to be this big one emerging off Africa this morning. This is certainly one of the most robust waves we’ve seen this season.

A robust tropical wave is emerging off Africa this morning. This may become a feature to watch as it transits the ocean, but modeling remains lukewarm at best on its development chances. (Weathernerds.org)

This wave’s future is a bit sketchy. Some modeling is warming to the idea of slow development next week, but the vast majority is cool to that chance. I would say that it’s an item to watch but unlikely to be an item of serious concern. We’ll see where we are on Monday with this one.

Fantasyland (beyond day 10): Nothing else of note

Really, things look pretty quiet outside of this wave off Africa and Don’s meanderings in the open Atlantic. Modeling is fairly calm for days 11 through 15. The European model’s extended output ticked back up activity odds a bit in weeks 3 and especially 4 yesterday. I think sometime around August 10th, give or take, it will be time to watch the big picture a bit closer. We shall see.

July 13, 2023 Outlook: Short-lived, open Atlantic Invest 94L is the only item on the board

One-sentence summary

A disturbance in the north-central Atlantic presently remains the only area of note over the next 7 to 10 days, and it will not threaten any land.

Happening now: Mid-ocean madness!

That subheading is a bit dramatic, but it’s been quiet enough of late, so we’ll let that go. Anyway, as we gaze upon the open Atlantic between Bermuda and the Azores this morning, we can see an area of cloudiness and storminess sitting over that part of the world. Yesterday, it received the invest designation, meaning meteorologists have enough evidence to run some additional modeling on this area.

Invest 94L is a heavily lopsided system with a 60 percent chance of becoming a depression over the next couple days before runs into problems and likely fizzles out (Weathernerds.org)

Invest 94L has about a 60 percent chance of developing over the next few days before it runs out of support in the open Atlantic. It will not threaten any land, and at worst, it should become a minimal tropical storm. Chaotic steering currents and a weak system will make 94L, whatever it becomes, susceptible to being bullied around, and as such, the potential track looks a bit like a horseshoe.

The track of Invest 94L will likely bring it north, then east, then south again as it meanders over the open Atlantic. It’s likely to fizzle out before day 5 or so. (Tropical Tidbits)

This type of track, odd as it seems, is not that uncommon in this part of the world. When storms develop out in the hinterlands of the basin, they can do weird things, because they are often and weak and just going to get pushed around by whatever influences exist at the time in those areas. We’ve seen storms do loop-de-loops, curly-Qs, stutter steps, somersaults (ok not really), and more. So, yes, it looks difficult to wrap your head around perhaps, but it’s not uncommon. That it is happening in mid-July does make it a bit uncommon, as we’ve discussed this week.

Anyway, over the next few days, 94L will possibly rev up, rev down, and eventually falter as it has to manage shear and cooler waters.

The medium-range (days 6 to 10): Nothing for now

There is nothing of note in the medium-range that we can see at this time. I will note, however, that one way to get a homebrew-type storm (a system that forms somewhat unexpectedly close to the coast) is to pile complexes of thunderstorms into the Gulf of Mexico. Over the next week or so, that’s sort of what we may see happen, as areas of thunderstorms meander around the eastern periphery of high pressure anchored over Texas and the Southwest.

The European operational model forecast of rainfall for the next week shows occasional areas of thunderstorms drifting across the Southeast and/or into the far northern Gulf. Normally, we’d keep tabs on these to be safe, but it does not look as though any of this will threaten development. (Pivotal Weather)

As of today, I see no reason to think that any of this would form. But with enough “oomph” it becomes something to watch. For now, that’s not expected, but I at least want to point it out to you so you can see a little more of what we look at and why we don’t just rip and read models verbatum.

Fantasyland (beyond day 10): Let’s look way out beyond day 10

As of today, nothing is showing up out there in the distant future. Things look quiet into most of days 10 to 15 or so.

The ECMWF model recently completed a major upgrade that allows a 100 member ensemble to run once a day to produce a forecast 3 to 6 weeks out in time. In other words, it runs the model 100 times with various tweaks to produce various outcomes. One product it does produce out 3 to 4 weeks is a tropical cyclone frequency and accumulated cyclone energy (ACE) forecast. I try not to read too much into these, as they can be somewhat noisy. Just this week, they suggested more activity in weeks 3 and 4. But as of yesterday’s run, that had backed off.

The ECMWF week 3 tropical storm frequency forecast shows the Atlantic about average for week 3, July 31st through August 6th. (ECMWF)

Still, it’s a nice tool to have. It currently shows near average activity for weeks 3 and 4, sort of what I would have expected when looking at the bigger picture right now. That is not to say that things cannot get active in that timeframe, just that sitting here today, we don’t necessarily expect it to happen. There are some hints that later in week 4 or week 5 (mid-August), we may see the Atlantic develop a more favorable “background state,” which could lead to a more hospitable environment for tropical systems. We will see how that progresses forward in time. For now, rest easy and enjoy the quiet!

July 12, 2023 Outlook: The Gulf of Mexico is blazing hot as we approach mid-July

One-sentence summary

The majority of the tropical Atlantic will remain fairly quiet, however it appears increasingly possible that a tropical system could form several hundred miles east of Bermuda during the next week.

Happening Now: No worries for most

In the Atlantic this week all eyes are, improbably, on an area of low pressure located about 500 miles to the east-northeast of Bermuda. As Matt pointed out on Tuesday, historically this is a very unlikely place for a tropical system to form in mid-July. But as we’ll discuss a bit more below, this is not a normal year. The seas in the Central Atlantic Ocean are fairly warm for this time of year.

All eyes, for now, are on the Central Atlantic Ocean. (NOAA)

The National Hurricane Center gives this system a 50 percent chance of becoming a tropical depression or storm over the next seven days before it would likely fizzle out, moving further north into waters less favorable for development. Given that this system almost certainly will remain out at sea, it should ultimately be of little concern to to us in terms of impacts. Unless you’re a fish. Or run a shipping company.

The medium range (days 6 to 10): Let’s talk about the Gulf of Mexico

Beyond the system in the Central Atlantic, there’s not much to say in terms of activity. But that’s perfectly normal for mid-July, when there’s often a lull in the tropics. However, I do think the warm water that’s allowing the Central Atlantic system to form offers us a cautionary tale.

If we turn our gaze to the Gulf of Mexico, we see very high sea surface temperatures. If you live anywhere along the coast, from Brownsville, Texas to Miami, Florida, you’ve probably noticed the very warm nights this summer. This is due, in part, to temperatures in the Gulf of Mexico that are running from 1 to 5 degrees Fahrenheit above normal. This onshore flow adds to the overall mugginess of the air.

Sea surface temperature anomaly in the Gulf of Mexico. (University of Miami)

This is not a concern now for tropical activity, as wind shear remains fairly robust across the Gulf, inhibiting storm formation. But it will become a significant concern as we get into August and September, when wind shear tends to relax a bit. I’m not making any concrete predictions here, but with sea surface temperatures this warm, if tropical systems do form they will have the potential to become very strong, very quickly.

Fantasyland (beyond day 10): Still quiet

Fortunately, there remains no sign of anything notable in the extended range right now. This is likely to change as we get toward the end of July and into August, but for now things are quiet.