July 18, 2023 Outlook: Calvin will bring heavy rain and gusty winds to Hawaii, especially the Big Island and Maui

One-sentence summary

Tropical Storm Calvin will bring impacts to Hawaii later today and tomorrow, while Don stirs in a slowly awakening Atlantic.

Happening now: Hawaii readying for impacts from Tropical Storm Calvin

This is typically going to be an Atlantic-focused tropical blog, but truth be told, when something interesting or notable is happening elsewhere, it behooves us to offer some insights. Enter: Calvin. We discussed Calvin yesterday, and today we will watch for a close pass near the Big Island of Hawaii.

Tropical Storm Calvin is en route to the Big Island of Hawaii and will bring varying impacts to the state tonight and tomorrow. (Weathernerds.org)

A Tropical Storm Warning was issued yesterday for the Big Island. From the satellite image above, you can see that Calvin is not greatly organized but it clearly has a lot of moisture as indicated by the bright colors on satellite. Right now, maximum winds are 45 mph, making Calvin a minimal tropical storm. But the combination of a weakening tropical storm, high pressure to the north, and some terrain will likely lead to a healthy wind event over many of the Hawaiian Islands, even those not under TS Warnings.

While Calvin is expected to weaken over the next day or two, it will still bring some decent winds to the islands, including those not currently under a Tropical Storm Warning. (NHC)

As the storm approaches Hawaii today, we’ll see rain pick up this evening (island time). Rain will be heavy at times on Tuesday night and Wednesday morning before slowly winding down Wednesday afternoon and evening. This will be a quick storm. For most populous locations, it will be a bit breezy with periods of rain. The heaviest rain and strongest winds will impact the Big Island and Maui. Wind gusts on Mauna Loa and Mauna Kea, as well as around Haleakalā on Maui are expected to be 50 to 65 mph, while at Hilo winds should gust to 40 mph. The Kona side of the Big Island will gust to about 30 mph. Elsewhere, we will see winds of wind advisory or high wind warning criteria in Maui County, as well as perhaps even in Oahu.

Higher rain totals are likely on the windward slopes of all the islands, but especially Maui and the Big Island. As much as 4 to 8 inches will fall, likely leading to areas of flooding. (NOAA)

Rain totals are expected to peak in the 4 to 8 inch range on the windward slopes of the Big Island and the North Shore and eastern portions of Maui, with lesser amounts on the other islands. Hilo will probably see 4 to 6 inches of rain, while the Kona side of the Big Island will see 1 to 2 inches or a bit less. Flooding is likely in spots, particularly on east and southeast facing slopes, and a Flood Watch is posted for Maui, Molokai, Lanai, Kahoolawe, and the Big Island. Conditions will calm some on Thursday and beyond.

Shifting back to the Atlantic, Subtropical Depression Don reformed into a Tropical Storm on Monday evening. It continues to meander in the open waters between Bermuda and the Azores, with maximum winds of 40 mph.

Tropical Storm Don will continue to meander in the open Atlantic. (NHC)

It remains no threat to land.

The medium range (days 6 to 10): Keeping an eye on the Main Development Region

Yesterday, we discussed the potential for a tropical wave emerging off Africa to maybe, possibly develop as it came west over the next week or so. There remains a bit of model support for this outcome, albeit not a ton. One thing that this or any wave right now will have to manage is Saharan dust.

The yellow, orange, and red colors on the image above indicate widespread areas of Saharan dust in the Atlantic. Some of that dust will impact the Caribbean Islands and likely eventually the US, but it will also impact tropical development too. (Univ of Wisconsin SSEC)

I believe this is our biggest dust outbreak of the season, and it will really hamper things a bit. So while I believe we should continue watching the MDR, and this wave near Africa in particular, it seems that this will be a bit of an uphill battle, especially over the next week or so. Also of note, this Saharan dust is going to overspread the islands in the Caribbean the next few days, arriving in South Florida by late tomorrow or Thursday and lingering into next week, as dust also works toward the U.S. Gulf Coast and Mexico.

Fantasyland (beyond day 10): Some stirring but no substance

We continue to see things stirring in the extended range, but there are no specific storms to hang our hat on in the modeling, with the exception of the wave mentioned above. That could perhaps be an issue if it develops for the day 10 or later period. But that’s really the only game in town right now, or at least the only one we can coherently point to at this time.

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!